On feat/gemini-branch-ux-polish: gemini ux-polish WIP: viewer-list/kick/notifications/tray (review baseline)

Entering View now grabs keyboard focus on the code field (once, via a
one-shot flag so it doesn't steal focus every frame), so the user can paste
or type the share code immediately without clicking into it first.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Cargo.toml

@@ -2,7 +2,7 @@
 name = "pixelpass"
 version = "0.1.0"
 edition = "2024"
-description = "P2P screen sharing CLI over iroh + ffmpeg"
+description = "P2P screen sharing CLI over iroh"
 license = "MIT OR Apache-2.0"
 publish = false
 
@@ -30,8 +30,20 @@ uuid = { version = "1", features = ["v4"] }
 iroh-tickets = "1.0.0-rc.0"
 dialoguer = { version = "0.12", default-features = false }
 arboard = { version = "3", default-features = false, features = ["wayland-data-control"] }
+ureq = { version = "3", default-features = false, features = ["rustls"] }
+toml = "1"
+chrono = { version = "0.4", default-features = false, features = ["clock", "serde"] }
+eframe = { version = "0.34.2", default-features = false, features = ["glow", "default_fonts", "wayland", "x11"], optional = true }
+tray-icon = { version = "0.24.0", optional = true }
+notify-rust = { version = "4.17.0", optional = true }
+gtk = { version = "0.18.2", optional = true }
 
 [profile.release]
 lto = "thin"
 codegen-units = 1
 strip = "symbols"
+
+[features]
+# Opt-in graphical front-end (pixelpass --gui). Default-off so the headless
+# build never pulls the GUI toolkit tree.
+gui = ["dep:eframe", "dep:tray-icon", "dep:notify-rust", "dep:gtk"]

README.md

@@ -0,0 +1,324 @@
+# pixelpass
+
+P2P screen sharing CLI for Linux. Single binary, hole-punched over
+[iroh](https://www.iroh.computer/) — no port forwarding, no signup, no
+server-side accounts. Hardware-encoded H.264 + AAC audio, viewed in
+mpv or VLC.
+
+Built for people who just want to show their screen to a friend
+without spinning up a Discord call or fighting with NAT.
+
+## Status
+
+**v0.1.0** — verified end-to-end on the public internet (LTE relay path,
+~2s latency, real carrier-grade NAT) as of 2026-05-20.
+
+Working:
+- Wayland capture via the screencast portal (KDE Plasma 6 confirmed; other
+  Wayland compositors with the portal should work but are untested)
+- X11 capture via `ximagesrc` (whole screen, or a single window with
+  `--window`); selected automatically, or forced with `--display-server x11`
+- VAAPI H.264 encode in GStreamer (RDNA3 confirmed; other VAAPI-capable
+  GPUs should work), with a software x264 fallback via `--no-hwencode`
+- Audio capture of the default sink's monitor, with optional per-app
+  routing (`--app <name>`)
+- `--repair` cleanup of orphaned PipeWire state left by a crashed host
+- iroh QUIC bi-stream tunnel, direct-UDP and relay paths both verified
+- Interactive Host/View menu with clipboard auto-copy and mpv/VLC picker
+- Headless mode for scripts (`pixelpass <ticket>`)
+- Multi-viewer fanout (default 2, configurable via `--max-viewers`;
+  shared gst pipeline, one broadcast channel per host)
+- First-run upstream bandwidth pre-flight, persisted to
+  `~/.config/pixelpass/config.toml` and used to auto-size the default
+  viewer cap
+- Quality presets (`--quality source|high|medium|low|auto`) that trade
+  resolution + bitrate for upload bandwidth, plus an `Auto` mode that
+  derives quality from the bandwidth pre-flight
+
+Not yet built (deferred, not blocking):
+- Per-monitor selection on a multi-monitor X11 host — `ximagesrc` grabs the
+  whole root canvas; single-monitor cropping needs xrandr region coords
+- `use-damage=true` CPU optimization for the X11 capture path
+
+## Quick start
+
+### Interactive (recommended)
+
+```sh
+pixelpass
+```
+
+On the host machine: pick "Host", share a monitor via the portal dialog,
+the ticket lands on your clipboard. Send it to your viewer however you
+like (chat, email, paste in a note). The same ticket works for multiple
+viewers up to your `--max-viewers` cap.
+
+The very first host launch offers a one-time upstream bandwidth test
+(~5 s, ~5 MB to Cloudflare's open speed-test endpoint) so it can pick
+a sensible default for the viewer cap. You can skip it and a
+conservative default (2 viewers) is used; re-run it later with
+`pixelpass --reconfigure`.
+
+On the viewer machine: run `pixelpass`, pick "View", paste the ticket,
+pick mpv or VLC. The player launches detached and the stream starts.
+
+### Headless
+
+```sh
+# host: prints a ticket on stdout, waits for a peer
+pixelpass
+
+# viewer: skips the menu
+pixelpass <ticket>
+# then run the printed mpv command in another terminal
+```
+
+### Graphical (optional)
+
+A small window front-end is available in builds compiled with the `gui`
+feature (see [Build](#build)):
+
+```sh
+pixelpass --gui
+```
+
+Host: pick quality / max-viewers / options, click **Start hosting**, and the
+share code appears with a copy button alongside a live viewer count. View:
+paste a code, pick mpv or VLC, click **Connect** and the player launches.
+
+The window is a thin driver — it runs the same headless `pixelpass` as a
+child process and reads its event stream, so the GUI is purely additive and
+the capture machinery is untouched by it. On a build without the feature,
+`--gui` prints a hint to rebuild with it.
+
+## Requirements
+
+- Linux (Wayland or X11; the backend is autodetected)
+- A VAAPI-capable GPU and the right driver:
+  - AMD: `libva-mesa-driver`
+  - Intel: `intel-media-driver` (modern iGPUs) or `intel-vaapi-driver` (older)
+  - NVIDIA: `libva-nvidia-driver` (untested)
+- `vainfo` from `libva-utils` should list at least one H.264 entrypoint
+- GStreamer with these plugin packages installed:
+  - `gstreamer`, `gst-plugins-base`, `gst-plugins-good`, `gst-plugins-bad`,
+    `gst-plugins-ugly`, `gst-libav`, `gst-plugin-va`, `gst-plugin-pipewire`
+- A player: `mpv` (recommended) or `vlc`
+- If you use VLC, two split plugin packages are also needed on Arch-family
+  distros — the base `vlc` package does not pull them in:
+  - `vlc-plugin-dvb` — provides the MPEG-TS demuxer (`libts_plugin.so`).
+    Without it, VLC can't parse the container.
+  - `vlc-plugin-ffmpeg` — provides the H.264 decoder
+    (`libavcodec_plugin.so`). Without it, VLC parses the container,
+    identifies the codec as H.264, then errors with
+    `Codec h264 ... is not supported`.
+  mpv ships its own decoder stack and doesn't share either dependency.
+- PipeWire (for screencast portal + audio capture)
+
+On Arch / CachyOS / EndeavourOS:
+
+```sh
+sudo pacman -S gstreamer gst-plugins-base gst-plugins-good gst-plugins-bad \
+               gst-plugins-ugly gst-libav gst-plugin-va gst-plugin-pipewire \
+               libva-utils mpv
+# plus your GPU's VAAPI driver
+# plus, if you want to use VLC instead of mpv:
+sudo pacman -S vlc vlc-plugin-dvb vlc-plugin-ffmpeg
+```
+
+If the viewer is running on battery, set the CPU governor to performance
+or balanced — power-saver can choke even hardware-decoded 1080p H.264.
+
+## Build
+
+```sh
+cargo build --release
+./target/release/pixelpass --help
+```
+
+`rustc` 1.95+ / edition 2024.
+
+The optional graphical front-end (`pixelpass --gui`) is behind a default-off
+cargo feature so the headless build stays lean (it pulls the egui/eframe
+windowing stack). Build it with:
+
+```sh
+cargo build --release --features gui
+```
+
+## How it works
+
+```
+  Host                                                          Viewer
+  ────                                                          ──────
+  Wayland portal (ashpd) ──> PipeWire fd ─┐   (X11: ximagesrc, no portal)
+                                          │
+                                          ▼
+              gst-launch: <source> -> videorate -> vah264enc/x264enc ->
+                          h264parse -> mpegtsmux
+                          (audio:    pulsesrc <sink>.monitor ->
+                                     avenc_aac -> aacparse ─┘)
+                              │ stdout
+                              ▼
+              tokio HTTP server (in-process, ~30 lines)
+                              │
+                              ▼
+              iroh QUIC bi-stream (ALPN pixelpass/0) ◄══════════►
+                                                                 │
+                                                                 ▼
+                                                  tokio TcpListener
+                                                  on 127.0.0.1:rand
+                                                                 │
+                                                                 ▼
+                                                  mpv / VLC HTTP client
+```
+
+The viewer's player connects to a localhost HTTP server, which is
+just one end of the iroh tunnel. The host's HTTP server sits on the
+other end and streams GStreamer's stdout (an MPEG-TS containing
+H.264 + AAC) through with no demux or remux.
+
+iroh handles NAT traversal: direct UDP if hole-punching succeeds,
+relay path otherwise. Both have been verified end-to-end.
+
+## Why these choices
+
+- **iroh over Holesail / dumbpipe / Tailscale**: single Rust dep, no Node
+  runtime, no signup, no daemon — fits the "one self-contained binary"
+  goal.
+- **GStreamer for capture/encode, not ffmpeg**: stride/format pitfalls
+  when bridging raw video between processes; one in-process pipeline
+  sidesteps them.
+- **In-process Rust HTTP server, not ffmpeg-as-server**: ffmpeg's
+  `-listen 1` is one-shot and probe-budget-sensitive; the Rust task is
+  pure passthrough with no codec assumptions.
+- **MPEG-TS over fragmented MP4**: every player on Linux handles it
+  out of the box. AV1-in-MPEG-TS was tried and is unworkable through
+  libavformat — if AV1 ever comes back, it has to ride a different
+  container.
+- **VAAPI H.264 over x264**: ~5% of one CPU core instead of ~50% on
+  the host's hardware.
+
+## Configuration
+
+`pixelpass` keeps a small TOML config at `~/.config/pixelpass/config.toml`
+(or the XDG equivalent). Right now it only stores the result of the
+bandwidth pre-flight:
+
+```toml
+[bandwidth]
+status = "measured"            # measured | skipped | failed | unmeasured
+upstream_mbps = 8.78           # safe estimate (raw * 0.8)
+measured_at = "2026-05-21T20:41:16Z"
+```
+
+- `pixelpass --reconfigure` re-runs the test (e.g. after an ISP change).
+- Deleting the file resets pixelpass to first-run state.
+- Skip is sticky — once you skip the test, pixelpass won't ask again
+  unless you reconfigure.
+
+## Audio
+
+By default pixelpass captures the default sink's monitor — the viewer
+hears whatever the host hears. `--app <name>` narrows that to a single
+application: pixelpass creates a per-PID null-sink and uses libpipewire to
+reroute matching `Stream/Output/Audio` nodes (by `application.name`) into
+it, so the viewer hears just that app instead of the whole desktop. In the
+interactive menu you can pick the app from a list of what's currently
+playing.
+
+Microphone capture is intentionally out of scope — pixelpass is a
+screen-share tool meant to be paired with a dedicated voice app (Mumble,
+TeamSpeak, Discord, …) for two-way talk.
+
+If a host crashes mid-session it can leave orphaned `pixelpass_capture_*`
+null-sinks and their paired loopbacks loaded in PipeWire. Run
+`pixelpass --repair` to unload them and exit.
+
+## Display server
+
+The capture backend is autodetected from the environment
+(`WAYLAND_DISPLAY` → Wayland, else `DISPLAY` → X11, else
+`XDG_SESSION_TYPE`). Override it with `--display-server wayland|x11` — for
+example to force the X11 path while running inside a Wayland session (an
+Xwayland or Xephyr `DISPLAY`).
+
+- **Wayland** goes through the screencast portal: a "Share Screen?" dialog
+  appears when the first viewer connects, and you pick the monitor (or
+  window, with `--window`) there.
+- **X11** uses `ximagesrc` and starts silently when the first viewer
+  connects — the ticket is the access control, there's no portal gate.
+  `--window` runs an `xwininfo` picker (click the window you want to
+  share); without it the whole root window is captured.
+
+Encoding is hardware VAAPI (`vah264enc`) by default. `--no-hwencode`
+switches to software x264 (`x264enc tune=zerolatency`) for hosts without a
+working VAAPI H.264 entrypoint — higher CPU, no GPU needed. This applies
+to both backends.
+
+## Multi-viewer
+
+One gst capture pipeline fans out to N concurrent viewers via a
+`tokio::sync::broadcast` channel. The same ticket is reusable: as long
+as a viewer is connected, capture stays alive; when the last one
+leaves, the pipeline tears down and the portal stops streaming. A new
+viewer connecting after that re-triggers the portal dialog.
+
+Capacity is bounded by upstream bandwidth (each viewer is its own
+encrypted egress). The default cap comes from the bandwidth pre-flight
+result; `--max-viewers <N>` overrides it. When the cap is hit,
+additional connections are politely refused with a "host is full"
+message and the host keeps running.
+
+For more viewers, drop the per-viewer bitrate: e.g. `pixelpass
+--bitrate 2500 --max-viewers 4` fits four 2.5 Mbps streams in roughly
+12 Mbps of upstream. The `--quality` presets below are the friendlier
+way to do the same thing.
+
+## Quality
+
+`--quality <preset>` bundles a max video height, bitrate, and framerate —
+resolution is a quality-per-bitrate knob, so the three only make sense
+together. Quality is **host-global**: one encode pipeline fans out to every
+viewer, so the sharer picks one quality for everyone (per-viewer quality
+would need per-viewer encodes, which kills the fanout).
+
+| Preset   | Max height        | Bitrate   | fps |
+|----------|-------------------|-----------|-----|
+| `source` | native (no scale) | 6000 kbps | 30  |
+| `high`   | 1080p             | 4000 kbps | 30  |
+| `medium` | 720p              | 2500 kbps | 30  |
+| `low`    | 480p              | 1000 kbps | 30  |
+| `auto`   | derived (below)   | derived   | 30  |
+
+`auto` (the default) picks the highest preset whose bitrate fits your
+measured safe upstream divided by the viewer cap — so quality is sized for
+the worst case, since it's baked in when capture starts and can't drop when
+a second viewer joins. With no `--max-viewers`, it sizes for a single
+viewer. If there's no bandwidth measurement yet, `auto` falls back to
+`medium` (run `pixelpass --reconfigure` to measure). In the interactive
+menu, omitting `--quality` shows a picker instead of assuming `auto`.
+
+Downscaling preserves the source aspect ratio with square pixels and snaps
+to even dimensions (H.264 requires them). Power users can override
+individual fields: `--max-height N`, `--bitrate N`, and `--framerate N`
+each take precedence over the chosen preset's value for that field.
+
+## Known limitations and gotchas
+
+- **VLC needs `vlc-plugin-dvb` and `vlc-plugin-ffmpeg`** on Arch-family
+  distros — the base `vlc` package doesn't pull these in, and missing
+  either one breaks playback (the first kills the demuxer, the second
+  kills the H.264 decoder). pixelpass warns at player-launch time if
+  either plugin isn't on disk. mpv doesn't share these dependencies.
+- **Audio echo** if the host plays the stream through speakers and
+  captures system audio — expected, the mic / monitor picks up the
+  playback. Headphones bypass it.
+- **Late joiners see ~2 s of garbage** before the next keyframe lets
+  their decoder lock. Expected behavior, not a bug.
+- **VAAPI driver must be package-tracked**, not an orphaned `.so` on
+  disk. mpv's `--hwdec=auto` silently falls back to software decode
+  otherwise, which then chokes on a low-power viewer.
+
+## License
+
+MIT OR Apache-2.0, your pick.

scripts/smoke-pipeline.sh

@@ -51,3 +51,39 @@ else
     echo "$MPV_LOG" | tail -30 | sed 's/^/        /'
     exit 1
 fi
+
+# ── quality-preset downscale check ────────────────────────────────────────
+# Mirrors the videoscale step host/pipeline.rs inserts for a non-Source preset:
+# AFTER videoconvert (scaling system-memory NV12, not the raw source format) and
+# pinned to an exact even WxH computed from the source size. A 16:9 source @
+# 480p wants width 853.3 -> 852 even. Asserts the negotiated size matches and
+# the encoder accepts it. Guards both the "even-width caveat" and the
+# negotiation/placement regression that squashed the picture.
+SCALED="${TMPDIR:-/tmp}/pixelpass-smoke-scaled-$$.ts"
+trap 'rm -f "$OUT" "$SCALED"' EXIT
+echo "[smoke] downscale check: 1920x1080 -> 852x480 (videoscale after videoconvert)"
+gst-launch-1.0 -q \
+    mpegtsmux name=mux ! queue ! filesink location="$SCALED" \
+    videotestsrc num-buffers=30 is-live=false \
+        ! video/x-raw,width=1920,height=1080,framerate=30/1 \
+        ! videorate ! video/x-raw,framerate=30/1 \
+        ! queue ! videoconvert ! video/x-raw,format=NV12 \
+        ! videoscale ! video/x-raw,format=NV12,width=852,height=480 \
+        ! vah264enc rate-control=cbr bitrate=1000 key-int-max=60 \
+        ! h264parse config-interval=-1 \
+        ! video/x-h264,stream-format=byte-stream,alignment=au ! mux. \
+    audiotestsrc num-buffers=47 is-live=false \
+        ! audioconvert ! audioresample ! audio/x-raw,rate=48000,channels=2 \
+        ! avenc_aac bitrate=128000 ! aacparse ! mux.
+
+SCALED_DIMS=$(ffprobe -v error -select_streams v:0 -show_entries stream=width,height \
+    -of csv=p=0 "$SCALED" | head -1)
+SCALED_W=${SCALED_DIMS%,*}
+SCALED_H=${SCALED_DIMS#*,}
+echo "        negotiated ${SCALED_W}x${SCALED_H}"
+if [[ "$SCALED_H" == "480" && $((SCALED_W % 2)) -eq 0 && "$SCALED_W" -lt 1920 ]]; then
+    echo "[smoke] PASS — downscale produced an even width below source (proportional)"
+else
+    echo "[smoke] FAIL: expected even width < 1920 at height 480, got ${SCALED_W}x${SCALED_H}"
+    exit 1
+fi

src/cli.rs

@@ -4,7 +4,7 @@ use clap::{Parser, ValueEnum};
 #[command(
     name = "pixelpass",
     version,
-    about = "P2P screen sharing over iroh + ffmpeg",
+    about = "P2P screen sharing over iroh",
     long_about = "Run with no arguments for an interactive Host/View menu. \
                   Pass a ticket positionally to skip the menu and view headlessly."
 )]
@@ -13,6 +13,12 @@ pub struct Cli {
     pub ticket: Option<String>,
 
     // ── host options ──────────────────────────────────────────────────
+    /// Run as host without the interactive menu. Equivalent to picking
+    /// "Host" in the menu, but headless — for scripting and the --gui
+    /// front-end, which drives this binary as a child process.
+    #[arg(long)]
+    pub host: bool,
+
     /// Pick a single window instead of the whole screen.
     #[arg(long)]
     pub window: bool,
@@ -21,29 +27,40 @@ pub struct Cli {
     #[arg(long, value_name = "NAME")]
     pub app: Option<String>,
 
-    /// Mix in the default microphone source.
-    #[arg(long)]
-    pub mic: bool,
-
     /// Override display server autodetection.
     #[arg(long, value_enum)]
     pub display_server: Option<DisplayServerArg>,
 
-    /// Encode bitrate in kbps.
-    #[arg(long, default_value_t = 6000)]
-    pub bitrate: u32,
+    /// Quality preset. Bundles a max video height, bitrate, and framerate.
+    /// `auto` derives them from the saved bandwidth pre-flight (falls back to
+    /// `medium` when no measurement exists). Defaults to `auto`; in the
+    /// interactive menu, omitting this shows a picker instead.
+    #[arg(long, value_enum)]
+    pub quality: Option<Quality>,
 
-    /// Capture framerate.
-    #[arg(long, default_value_t = 30)]
-    pub framerate: u32,
+    /// Cap the encoded video height (px); width follows the source aspect.
+    /// Power-user override — takes precedence over the preset's height.
+    #[arg(long, value_name = "N")]
+    pub max_height: Option<u32>,
+
+    /// Encode bitrate in kbps. Overrides the quality preset's bitrate.
+    #[arg(long)]
+    pub bitrate: Option<u32>,
+
+    /// Capture framerate. Overrides the quality preset's framerate.
+    #[arg(long)]
+    pub framerate: Option<u32>,
 
     /// Disable VAAPI HW encode; force software x264.
     #[arg(long)]
     pub no_hwencode: bool,
 
-    /// Use low-latency SRT transport instead of HTTP MPEG-TS (Phase 2/3).
+    /// Maximum number of concurrent viewers. Additional connections are
+    /// politely refused with a "host full" message. Defaults to the
+    /// connection-aware recommendation from the bandwidth pre-flight if
+    /// available, otherwise 2.
     #[arg(long)]
-    pub low_latency: bool,
+    pub max_viewers: Option<u32>,
 
     // ── viewer options ────────────────────────────────────────────────
     /// Local TCP port for the viewer to expose (default: random).
@@ -51,6 +68,17 @@ pub struct Cli {
     pub port: u16,
 
     // ── global ────────────────────────────────────────────────────────
+    /// Launch the graphical front-end (a window with Host/View controls)
+    /// instead of the terminal menu. Requires a build with `--features gui`.
+    #[arg(long)]
+    pub gui: bool,
+
+    /// Emit machine-readable events on stdout (one JSON object per line)
+    /// alongside the human banner on stderr. For scripts and the --gui
+    /// front-end. Currently only `json` is supported.
+    #[arg(long, value_enum, value_name = "FORMAT")]
+    pub output: Option<OutputFormat>,
+
     /// Trace-level logging.
     #[arg(long, short)]
     pub verbose: bool,
@@ -58,6 +86,12 @@ pub struct Cli {
     /// Clean up orphaned PipeWire state from a crashed host run, then exit.
     #[arg(long)]
     pub repair: bool,
+
+    /// Re-run the bandwidth pre-flight test, save the result, then exit.
+    /// Use this if your connection has changed (new ISP, moved house, etc.)
+    /// or if the previously saved test result is stale.
+    #[arg(long)]
+    pub reconfigure: bool,
 }
 
 #[derive(ValueEnum, Clone, Copy, Debug)]
@@ -66,16 +100,45 @@ pub enum DisplayServerArg {
     X11,
 }
 
+#[derive(ValueEnum, Clone, Copy, Debug, PartialEq, Eq)]
+pub enum OutputFormat {
+    /// One JSON object per line on stdout.
+    Json,
+}
+
+/// Quality preset. Each fixed preset bundles a (max-height, bitrate, fps)
+/// tuple — resolution is a quality-per-bitrate knob, so the three only make
+/// sense together. `Auto` has no fixed tuple; it picks one of the others from
+/// the bandwidth pre-flight at host startup. See `host::quality`.
+#[derive(ValueEnum, Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Quality {
+    /// Native source resolution, 6000 kbps, 30 fps (no downscale).
+    Source,
+    /// Up to 1080p, 4000 kbps, 30 fps.
+    High,
+    /// Up to 720p, 2500 kbps, 30 fps.
+    Medium,
+    /// Up to 480p, 1000 kbps, 30 fps.
+    Low,
+    /// Derive from the measured upstream; falls back to `medium` when unmeasured.
+    Auto,
+}
+
 #[derive(Debug, Clone)]
 pub struct HostOpts {
     pub window: bool,
     pub app: Option<String>,
-    pub mic: bool,
     pub display_server: Option<DisplayServerArg>,
-    pub bitrate: u32,
-    pub framerate: u32,
+    /// Chosen preset (Auto = derive at startup). Defaults to Auto.
+    pub quality: Quality,
+    /// Raw `--bitrate` override (kbps); None = use the preset's bitrate.
+    pub bitrate: Option<u32>,
+    /// Raw `--framerate` override; None = use the preset's framerate.
+    pub framerate: Option<u32>,
+    /// Raw `--max-height` override (px); None = use the preset's height.
+    pub max_height: Option<u32>,
     pub no_hwencode: bool,
-    pub low_latency: bool,
+    pub max_viewers: Option<u32>,
     pub interactive: bool,
 }
 
@@ -90,12 +153,15 @@ impl Cli {
         HostOpts {
             window: self.window,
             app: self.app,
-            mic: self.mic,
             display_server: self.display_server,
+            // No `--quality` and nothing picked interactively → the documented
+            // default, Auto.
+            quality: self.quality.unwrap_or(Quality::Auto),
             bitrate: self.bitrate,
             framerate: self.framerate,
+            max_height: self.max_height,
             no_hwencode: self.no_hwencode,
-            low_latency: self.low_latency,
+            max_viewers: self.max_viewers,
             interactive,
         }
     }

src/common/bandwidth.rs

@@ -0,0 +1,73 @@
+//! One-shot upstream bandwidth measurement against Cloudflare's open
+//! speed-test endpoint. POST a fixed payload, time it, derive Mbps.
+//!
+//! Run via `tokio::task::spawn_blocking` from async contexts — ureq is a
+//! blocking client and we don't want to wedge the tokio runtime during
+//! the test.
+
+use anyhow::{Context, Result};
+use std::time::{Duration, Instant};
+
+const ENDPOINT: &str = "https://speed.cloudflare.com/__up";
+const PAYLOAD_BYTES: usize = 5 * 1024 * 1024; // 5 MiB
+const HTTP_TIMEOUT: Duration = Duration::from_secs(30);
+/// Multiplier applied to the raw measurement. TCP slow-start, ramp-up, and
+/// real-world contention all mean a one-shot upstream test slightly
+/// overestimates sustainable throughput; clamp to 80% for headroom.
+const SAFETY_FACTOR: f64 = 0.80;
+
+/// Result of a successful measurement.
+#[derive(Debug, Clone)]
+pub struct Measurement {
+    /// Raw measured throughput in megabits per second.
+    pub raw_mbps: f64,
+    /// `raw_mbps * SAFETY_FACTOR` — the value to use when sizing things.
+    pub safe_mbps: f64,
+    /// How long the upload took.
+    pub elapsed: Duration,
+}
+
+/// Blocking upload-speed test. Call from a `spawn_blocking` task.
+pub fn measure_upstream_blocking() -> Result<Measurement> {
+    let payload = vec![0u8; PAYLOAD_BYTES];
+    let agent = ureq::Agent::config_builder()
+        .timeout_global(Some(HTTP_TIMEOUT))
+        .build()
+        .new_agent();
+
+    let start = Instant::now();
+    let response = agent
+        .post(ENDPOINT)
+        .content_type("application/octet-stream")
+        .send(&payload[..])
+        .context("upload request to Cloudflare failed")?;
+    let elapsed = start.elapsed();
+
+    let status = response.status();
+    if !status.is_success() {
+        anyhow::bail!("Cloudflare returned HTTP {status}");
+    }
+
+    let bits = (PAYLOAD_BYTES as f64) * 8.0;
+    let seconds = elapsed.as_secs_f64().max(0.001);
+    let raw_mbps = bits / seconds / 1_000_000.0;
+    let safe_mbps = raw_mbps * SAFETY_FACTOR;
+
+    Ok(Measurement {
+        raw_mbps,
+        safe_mbps,
+        elapsed,
+    })
+}
+
+/// Convert a safe-upstream Mbps figure plus the host's per-viewer bitrate
+/// (kbps for video, ignoring audio + protocol overhead which we account for
+/// via SAFETY_FACTOR) into a recommended viewer count. Floors to at least 1.
+pub fn recommended_max_viewers(safe_mbps: f64, bitrate_kbps: u32) -> u32 {
+    let per_viewer_mbps = (bitrate_kbps as f64) / 1000.0;
+    if per_viewer_mbps <= 0.0 {
+        return 1;
+    }
+    let n = (safe_mbps / per_viewer_mbps).floor();
+    if n < 1.0 { 1 } else { n as u32 }
+}

src/common/config.rs

@@ -0,0 +1,101 @@
+//! Persistent user-level config at `~/.config/pixelpass/config.toml`.
+//!
+//! Right now this only tracks the bandwidth pre-flight result. Future
+//! preferences (default player, default bitrate, etc.) can hang off the
+//! same file under their own `[section]`.
+
+use anyhow::{Context, Result};
+use chrono::{DateTime, Utc};
+use directories::ProjectDirs;
+use serde::{Deserialize, Serialize};
+use std::fs;
+use std::io::Write;
+use std::path::PathBuf;
+
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct Config {
+    #[serde(default)]
+    pub bandwidth: BandwidthEntry,
+}
+
+/// Result of the first-run upstream measurement.
+///
+/// `status = "unmeasured"` means we've never asked the user — show the
+/// first-run dialog. `"measured"` means we have a number. `"skipped"`
+/// means the user opted out (sticky — don't ask again). `"failed"`
+/// means the last attempt errored and we should ask the user on next
+/// interactive launch whether to retry.
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct BandwidthEntry {
+    #[serde(default = "default_status")]
+    pub status: BandwidthStatus,
+    #[serde(default)]
+    pub upstream_mbps: Option<f64>,
+    #[serde(default)]
+    pub measured_at: Option<DateTime<Utc>>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum BandwidthStatus {
+    Unmeasured,
+    Measured,
+    Skipped,
+    Failed,
+}
+
+impl Default for BandwidthStatus {
+    fn default() -> Self {
+        Self::Unmeasured
+    }
+}
+
+fn default_status() -> BandwidthStatus {
+    BandwidthStatus::Unmeasured
+}
+
+/// Returns `~/.config/pixelpass/config.toml` (or the XDG equivalent on other
+/// platforms). The parent directory is created lazily by [`save`].
+pub fn config_path() -> Result<PathBuf> {
+    let dirs = ProjectDirs::from("", "", "pixelpass")
+        .context("could not locate a config directory for pixelpass")?;
+    Ok(dirs.config_dir().join("config.toml"))
+}
+
+/// Returns the loaded config, or a `Default` instance if the file doesn't
+/// exist yet. Bubble up parse errors so we don't silently overwrite a
+/// hand-edited config the user is debugging.
+pub fn load() -> Result<Config> {
+    let path = config_path()?;
+    match fs::read_to_string(&path) {
+        Ok(s) => toml::from_str::<Config>(&s)
+            .with_context(|| format!("failed to parse {}", path.display())),
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(Config::default()),
+        Err(e) => Err(e).with_context(|| format!("failed to read {}", path.display())),
+    }
+}
+
+/// Atomic write via tempfile-in-same-dir + rename.
+pub fn save(cfg: &Config) -> Result<()> {
+    let path = config_path()?;
+    let parent = path
+        .parent()
+        .context("config path has no parent directory")?;
+    fs::create_dir_all(parent)
+        .with_context(|| format!("failed to create {}", parent.display()))?;
+
+    let serialized =
+        toml::to_string_pretty(cfg).context("failed to serialize config to TOML")?;
+
+    let tmp = parent.join(format!(".config.toml.tmp.{}", std::process::id()));
+    {
+        let mut f = fs::File::create(&tmp)
+            .with_context(|| format!("failed to create {}", tmp.display()))?;
+        f.write_all(serialized.as_bytes())
+            .with_context(|| format!("failed to write {}", tmp.display()))?;
+        f.sync_all().ok();
+    }
+    fs::rename(&tmp, &path)
+        .with_context(|| format!("failed to rename {} -> {}", tmp.display(), path.display()))?;
+    Ok(())
+}

src/common/deps.rs

@@ -2,21 +2,49 @@ use anyhow::{Result, bail};
 use std::path::PathBuf;
 use std::process::Command;
 
+use crate::cli::HostOpts;
 use crate::common::display::DisplayServer;
 
-pub fn check_host_binaries(display: DisplayServer) -> Result<()> {
-    if display == DisplayServer::Wayland {
-        require("gst-launch-1.0")?;
-        require("gst-inspect-1.0")?;
-        require("pactl")?;
-        require_gst_element("pipewiresrc")?;
-        require_gst_element("vah264enc")?;
-        require_gst_element("h264parse")?;
-        require_gst_element("mpegtsmux")?;
-        require_gst_element("pulsesrc")?;
-        require_gst_element("avenc_aac")?;
-        require_gst_element("aacparse")?;
+pub fn check_host_binaries(display: DisplayServer, opts: &HostOpts) -> Result<()> {
+    // Unknown is handled (and rejected) by the caller; nothing to check here.
+    if display == DisplayServer::Unknown {
+        return Ok(());
     }
+
+    // Shared across both backends: the gst tools, audio routing, and the
+    // encode/mux tail elements.
+    require("gst-launch-1.0")?;
+    require("gst-inspect-1.0")?;
+    require("pactl")?;
+    // videoscale (downscale for the quality presets) lives in plugins-base,
+    // the same package the gst tools need, so this rarely fails on its own —
+    // but check it for a clear error if a partial install is missing it.
+    require_gst_element("videoscale")?;
+    require_gst_element("h264parse")?;
+    require_gst_element("mpegtsmux")?;
+    require_gst_element("pulsesrc")?;
+    require_gst_element("avenc_aac")?;
+    require_gst_element("aacparse")?;
+
+    // Encoder depends on --no-hwencode (software x264 vs hardware VAAPI).
+    if opts.no_hwencode {
+        require_gst_element("x264enc")?;
+    } else {
+        require_gst_element("vah264enc")?;
+    }
+
+    // Per-backend video source, plus the X11 window-picker when --window is set.
+    match display {
+        DisplayServer::Wayland => require_gst_element("pipewiresrc")?,
+        DisplayServer::X11 => {
+            require_gst_element("ximagesrc")?;
+            if opts.window {
+                require("xwininfo")?;
+            }
+        }
+        DisplayServer::Unknown => unreachable!("early-returned above"),
+    }
+
     Ok(())
 }
 
@@ -69,6 +97,13 @@ fn install_hint_for_bin(bin: &str) -> String {
             Some("opensuse" | "opensuse-tumbleweed" | "opensuse-leap") => "pulseaudio-utils",
             _ => "pulseaudio-utils (provides `pactl`)",
         },
+        "xwininfo" => match distro.as_deref() {
+            Some("arch" | "cachyos" | "manjaro" | "endeavouros") => "xorg-xwininfo",
+            Some("debian" | "ubuntu" | "pop" | "linuxmint") => "x11-utils",
+            Some("fedora" | "nobara") => "xorg-x11-utils",
+            Some("opensuse" | "opensuse-tumbleweed" | "opensuse-leap") => "xwininfo",
+            _ => "xwininfo (X11 window-info utility)",
+        },
         _ => bin,
     };
     install_command(&distro, pkg)
@@ -91,6 +126,27 @@ fn install_hint_for_gst_element(name: &str) -> String {
             Some("opensuse" | "opensuse-tumbleweed" | "opensuse-leap") => "gstreamer-plugins-bad",
             _ => "the GStreamer VA-API plugin (requires an H.264-capable GPU; almost all modern GPUs)",
         },
+        "x264enc" => match distro.as_deref() {
+            Some("arch" | "cachyos" | "manjaro" | "endeavouros") => "gst-plugins-ugly",
+            Some("debian" | "ubuntu" | "pop" | "linuxmint") => "gstreamer1.0-plugins-ugly",
+            Some("fedora" | "nobara") => "gstreamer1-plugins-ugly",
+            Some("opensuse" | "opensuse-tumbleweed" | "opensuse-leap") => "gstreamer-plugins-ugly",
+            _ => "the GStreamer x264 plugin (plugins-ugly)",
+        },
+        "ximagesrc" => match distro.as_deref() {
+            Some("arch" | "cachyos" | "manjaro" | "endeavouros") => "gst-plugins-good",
+            Some("debian" | "ubuntu" | "pop" | "linuxmint") => "gstreamer1.0-plugins-good",
+            Some("fedora" | "nobara") => "gstreamer1-plugins-good",
+            Some("opensuse" | "opensuse-tumbleweed" | "opensuse-leap") => "gstreamer-plugins-good",
+            _ => "the GStreamer X11 plugin (plugins-good)",
+        },
+        "videoscale" => match distro.as_deref() {
+            Some("arch" | "cachyos" | "manjaro" | "endeavouros") => "gst-plugins-base",
+            Some("debian" | "ubuntu" | "pop" | "linuxmint") => "gstreamer1.0-plugins-base",
+            Some("fedora" | "nobara") => "gstreamer1-plugins-base",
+            Some("opensuse" | "opensuse-tumbleweed" | "opensuse-leap") => "gstreamer-plugins-base",
+            _ => "the GStreamer plugins-base set",
+        },
         "h264parse" | "mpegtsmux" | "aacparse" => match distro.as_deref() {
             Some("arch" | "cachyos" | "manjaro" | "endeavouros") => "gst-plugins-bad",
             Some("debian" | "ubuntu" | "pop" | "linuxmint") => "gstreamer1.0-plugins-bad",

src/common/mod.rs

@@ -1,6 +1,9 @@
 pub mod alpn;
+pub mod bandwidth;
+pub mod config;
 pub mod deps;
 pub mod display;
+pub mod output;
 pub mod process;
 pub mod signal;
 pub mod tunnel;

src/common/output.rs

@@ -0,0 +1,81 @@
+//! Machine-readable event stream for non-interactive front-ends.
+//!
+//! When enabled with `--output json`, the host and viewer emit one JSON
+//! object per line on **stdout**. The human banner and `tracing` logs stay
+//! on **stderr**, so the two streams never interleave and a parser reading
+//! stdout sees only events. Each line is flushed immediately so a front-end
+//! reading the pipe gets events live rather than in block-buffered chunks.
+//!
+//! This is the shell-out counterpart to an in-process event channel: the
+//! `--gui` front-end re-execs this binary as `pixelpass --host --output json`
+//! and parses these lines to drive its window.
+
+use std::io::Write;
+use std::sync::atomic::{AtomicBool, Ordering};
+
+use serde::Serialize;
+
+static JSON_ENABLED: AtomicBool = AtomicBool::new(false);
+
+/// Turn JSON event output on. Called once at startup from `--output json`.
+pub fn set_json(enabled: bool) {
+    JSON_ENABLED.store(enabled, Ordering::Relaxed);
+}
+
+fn json_enabled() -> bool {
+    JSON_ENABLED.load(Ordering::Relaxed)
+}
+
+/// One event in the stdout stream. Serialized as `{"event":"<tag>", ...}`.
+#[derive(Serialize)]
+#[serde(tag = "event", rename_all = "snake_case")]
+pub enum Event<'a> {
+    /// The relay-only ticket the viewer needs. Emitted once at host startup.
+    Ticket { value: &'a str },
+    /// One-shot host configuration summary, mirroring the banner fields.
+    HostInfo {
+        display_server: &'a str,
+        capture: &'a str,
+        quality: &'a str,
+        dimensions: &'a str,
+        hw_encode: bool,
+        max_viewers: u32,
+        max_viewers_source: &'a str,
+    },
+    /// A new viewer joined.
+    ViewerJoined { id: &'a str, active: u32, max: u32 },
+    /// A viewer disconnected.
+    ViewerLeft { id: &'a str, active: u32, max: u32 },
+    /// Capture pipeline lifecycle (spawned on first viewer, torn down on last).
+    Capture { state: CaptureState },
+    /// A viewer was turned away (host full, or capture spawn failed).
+    ViewerRefused { reason: &'a str },
+    /// Viewer-side: the local player URL is ready to open.
+    Connected { url: &'a str },
+}
+
+#[derive(Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum CaptureState {
+    Started,
+    Stopped,
+}
+
+/// Emit one event as a JSON line on stdout, flushed. No-op unless JSON
+/// output was enabled with [`set_json`], so call sites can sprinkle these
+/// unconditionally without branching.
+pub fn emit(event: Event) {
+    if !json_enabled() {
+        return;
+    }
+    match serde_json::to_string(&event) {
+        Ok(line) => {
+            let mut out = std::io::stdout().lock();
+            // Best-effort: a closed pipe (front-end gone) shouldn't crash the
+            // host — it keeps streaming to any viewers already connected.
+            let _ = writeln!(out, "{line}");
+            let _ = out.flush();
+        }
+        Err(e) => tracing::warn!("failed to serialize event: {e}"),
+    }
+}

src/gui/child.rs

@@ -0,0 +1,259 @@
+//! Drives a headless `pixelpass` child process for the GUI.
+//!
+//! The GUI re-execs this same binary (via [`std::env::current_exe`]) in
+//! headless mode with `--output json`, then reads the child's JSON event
+//! stream on a background thread and forwards parsed events over a channel the
+//! egui app drains each frame. stderr is captured into a small ring so a
+//! failed launch (e.g. a missing gst plugin) can be surfaced in the window.
+
+use std::io::{BufRead, BufReader};
+use std::process::{Child, Command, Stdio};
+use std::sync::mpsc::Receiver;
+use std::sync::{Arc, Mutex};
+use std::time::Duration;
+
+use eframe::egui;
+use nix::sys::signal::{Signal, kill};
+use nix::unistd::Pid;
+use serde::Deserialize;
+
+/// One parsed event from the child's stdout. Owned mirror of
+/// [`crate::common::output::Event`] (which borrows for emit); kept separate so
+/// the wire format and the parser can evolve independently.
+#[derive(Deserialize, Debug)]
+#[serde(tag = "event", rename_all = "snake_case")]
+pub enum ChildEvent {
+    Ticket {
+        value: String,
+    },
+    HostInfo {
+        display_server: String,
+        capture: String,
+        quality: String,
+        dimensions: String,
+        hw_encode: bool,
+        max_viewers: u32,
+        max_viewers_source: String,
+    },
+    ViewerJoined {
+        id: String,
+        active: u32,
+        max: u32,
+    },
+    ViewerLeft {
+        id: String,
+        active: u32,
+        max: u32,
+    },
+    Capture {
+        state: CaptureState,
+    },
+    ViewerRefused {
+        reason: String,
+    },
+    Connected {
+        url: String,
+    },
+}
+
+#[derive(Deserialize, Debug, Clone, Copy, PartialEq)]
+#[serde(rename_all = "snake_case")]
+pub enum CaptureState {
+    Started,
+    Stopped,
+}
+
+const STDERR_TAIL_MAX: usize = 60;
+
+pub struct ChildProc {
+    child: Child,
+    pub rx: Receiver<ChildEvent>,
+    stderr_tail: Arc<Mutex<Vec<String>>>,
+    stdin: std::process::ChildStdin,
+}
+
+impl ChildProc {
+    /// Spawn `pixelpass <args>` as a child, wiring up the event reader. `ctx`
+    /// is repainted whenever an event arrives so the UI updates live.
+    pub fn spawn(args: &[String], ctx: egui::Context) -> std::io::Result<Self> {
+        let exe = std::env::current_exe()?;
+        let mut child = Command::new(exe)
+            .args(args)
+            .stdin(Stdio::piped())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::piped())
+            .spawn()?;
+
+        let (tx, rx) = std::sync::mpsc::channel();
+        let stdin = child.stdin.take().expect("stdin piped");
+        let stdout = child.stdout.take().expect("stdout piped");
+        std::thread::spawn(move || {
+            let reader = BufReader::new(stdout);
+            for line in reader.lines().map_while(Result::ok) {
+                if line.trim().is_empty() {
+                    continue;
+                }
+                // Ignore any non-event line rather than dropping the stream.
+                if let Ok(ev) = serde_json::from_str::<ChildEvent>(&line) {
+                    if tx.send(ev).is_err() {
+                        break; // app gone
+                    }
+                    ctx.request_repaint();
+                }
+            }
+        });
+
+        let stderr_tail = Arc::new(Mutex::new(Vec::<String>::new()));
+        let stderr = child.stderr.take().expect("stderr piped");
+        let tail = stderr_tail.clone();
+        std::thread::spawn(move || {
+            let reader = BufReader::new(stderr);
+            for line in reader.lines().map_while(Result::ok) {
+                let mut t = tail.lock().unwrap();
+                t.push(line);
+                let overflow = t.len().saturating_sub(STDERR_TAIL_MAX);
+                if overflow > 0 {
+                    t.drain(0..overflow);
+                }
+            }
+        });
+
+        Ok(Self {
+            child,
+            rx,
+            stderr_tail,
+            stdin,
+        })
+    }
+
+    /// Whether the child is still running.
+    pub fn is_alive(&mut self) -> bool {
+        matches!(self.child.try_wait(), Ok(None))
+    }
+
+    /// The last captured stderr lines, joined — for error display.
+    pub fn stderr_tail(&self) -> String {
+        self.stderr_tail.lock().unwrap().join("\n")
+    }
+
+    /// Send a newline-terminated command to the child.
+    pub fn send_command(&mut self, cmd: &str) {
+        use std::io::Write;
+        if let Err(e) = writeln!(self.stdin, "{cmd}") {
+            tracing::warn!("failed to send command to child: {e}");
+        }
+    }
+
+    /// Gracefully stop the child: SIGINT (so the host runs its ctrl-c teardown
+    /// — tears down capture, closes the endpoint), with a ~2 s grace period
+    /// before a hard kill. Idempotent.
+    pub fn stop(&mut self) {
+        if matches!(self.child.try_wait(), Ok(Some(_))) {
+            return; // already exited
+        }
+        let _ = kill(Pid::from_raw(self.child.id() as i32), Signal::SIGINT);
+        for _ in 0..40 {
+            if matches!(self.child.try_wait(), Ok(Some(_))) {
+                return;
+            }
+            std::thread::sleep(Duration::from_millis(50));
+        }
+        let _ = self.child.kill();
+        let _ = self.child.wait();
+    }
+}
+
+impl Drop for ChildProc {
+    fn drop(&mut self) {
+        // Closing the window (dropping the app, hence the session) must not
+        // orphan a live host child streaming to viewers.
+        self.stop();
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::common::output::{CaptureState as EmitState, Event};
+
+    // The GUI parses what the headless child emits. These round-trip the
+    // emitter's own types (`common::output::Event`) through the parser
+    // (`ChildEvent`) so a rename on either side of the wire fails here rather
+    // than silently breaking the GUI at runtime.
+    fn parse(emit: Event) -> ChildEvent {
+        let line = serde_json::to_string(&emit).unwrap();
+        serde_json::from_str::<ChildEvent>(&line).unwrap()
+    }
+
+    #[test]
+    fn ticket_round_trips() {
+        assert!(matches!(
+            parse(Event::Ticket { value: "endpointXYZ" }),
+            ChildEvent::Ticket { value } if value == "endpointXYZ"
+        ));
+    }
+
+    #[test]
+    fn host_info_round_trips() {
+        let ev = parse(Event::HostInfo {
+            display_server: "Wayland",
+            capture: "fullscreen + system-audio",
+            quality: "Medium",
+            dimensions: "≤720p / 2500 kbps / 30 fps",
+            hw_encode: true,
+            max_viewers: 3,
+            max_viewers_source: "user-specified",
+        });
+        match ev {
+            ChildEvent::HostInfo {
+                display_server,
+                quality,
+                hw_encode,
+                max_viewers,
+                ..
+            } => {
+                assert_eq!(display_server, "Wayland");
+                assert_eq!(quality, "Medium");
+                assert!(hw_encode);
+                assert_eq!(max_viewers, 3);
+            }
+            other => panic!("expected HostInfo, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn viewer_events_round_trips() {
+        assert!(matches!(
+            parse(Event::ViewerJoined { id: "nodeXYZ", active: 2, max: 4 }),
+            ChildEvent::ViewerJoined { id, active: 2, max: 4 } if id == "nodeXYZ"
+        ));
+        assert!(matches!(
+            parse(Event::ViewerLeft { id: "nodeXYZ", active: 1, max: 4 }),
+            ChildEvent::ViewerLeft { id, active: 1, max: 4 } if id == "nodeXYZ"
+        ));
+    }
+
+    #[test]
+    fn capture_state_round_trips() {
+        assert!(matches!(
+            parse(Event::Capture { state: EmitState::Started }),
+            ChildEvent::Capture { state: CaptureState::Started }
+        ));
+        assert!(matches!(
+            parse(Event::Capture { state: EmitState::Stopped }),
+            ChildEvent::Capture { state: CaptureState::Stopped }
+        ));
+    }
+
+    #[test]
+    fn refused_and_connected_round_trip() {
+        assert!(matches!(
+            parse(Event::ViewerRefused { reason: "host is full" }),
+            ChildEvent::ViewerRefused { reason } if reason == "host is full"
+        ));
+        assert!(matches!(
+            parse(Event::Connected { url: "http://127.0.0.1:5000" }),
+            ChildEvent::Connected { url } if url == "http://127.0.0.1:5000"
+        ));
+    }
+}

src/gui/mod.rs

@@ -0,0 +1,881 @@
+//! Graphical front-end (`pixelpass --gui`), compiled only with the `gui`
+//! feature.
+//!
+//! Architecture: this window is a thin **shell-out** driver. It never touches
+//! the capture / portal / gst / iroh machinery directly — instead it re-execs
+//! this same binary in headless mode (`pixelpass --host --output json …` or
+//! `pixelpass <ticket> --output json`) as a child process and parses the
+//! child's JSON event stream (see [`crate::common::output`]) to drive what it
+//! shows. That keeps the fragile capture stack sealed in a separate process:
+//! the GUI can be closed or crash without taking a live stream down.
+
+mod child;
+
+use eframe::egui;
+
+use self::child::{ChildEvent, ChildProc};
+
+/// Launch the GUI event loop. Blocks until the window is closed. Runs on the
+/// main thread (a winit requirement), which is where `main` calls it from.
+pub fn run() -> anyhow::Result<()> {
+    let options = eframe::NativeOptions {
+        viewport: egui::ViewportBuilder::default()
+            .with_inner_size([520.0, 480.0])
+            .with_min_inner_size([460.0, 380.0])
+            .with_title("PixelPass"),
+        ..Default::default()
+    };
+
+    eframe::run_native(
+        "PixelPass",
+        options,
+        Box::new(|_cc| Ok(Box::new(PixelPassApp::default()))),
+    )
+    .map_err(|e| anyhow::anyhow!("GUI failed to start: {e}"))
+}
+
+/// Best-effort clipboard write. Returns whether it succeeded so callers can
+/// show an honest "✓ Copied" / fallback hint (the clipboard can be flaky on
+/// Wayland, and a silent miss is what left users pasting stale tickets).
+fn set_clipboard(text: &str) -> bool {
+    arboard::Clipboard::new()
+        .and_then(|mut cb| cb.set_text(text.to_owned()))
+        .is_ok()
+}
+
+/// Best-effort clipboard read, backing the viewer Paste button and the
+/// View-screen prefill. `None` on a flaky/empty clipboard — callers just leave
+/// the field untouched.
+fn get_clipboard() -> Option<String> {
+    arboard::Clipboard::new()
+        .and_then(|mut cb| cb.get_text())
+        .ok()
+}
+
+/// Decode the host endpoint id from a ticket string, using the exact same
+/// parse the viewer does (`EndpointTicket::from_str`), so the GUI agrees with
+/// the child about what's a valid code. `None` means it isn't a pixelpass
+/// ticket at all. Used to surface a stale/garbage paste *before* the 15s
+/// connect timeout, and to show which host the viewer is dialing — the missing
+/// signal that let people repeatedly dial a long-dead host.
+fn ticket_endpoint_id(ticket: &str) -> Option<String> {
+    ticket
+        .trim()
+        .parse::<iroh_tickets::endpoint::EndpointTicket>()
+        .ok()
+        .map(|t| t.endpoint_addr().id.to_string())
+}
+
+/// Eyeball-comparable short form of an endpoint id (full ids are long). Enough
+/// to spot that two ids differ; the host and viewer screens show the same
+/// truncation so a stale ticket reads as an obvious mismatch.
+fn short_id(id: &str) -> String {
+    let prefix: String = id.chars().take(12).collect();
+    if prefix.len() < id.len() {
+        format!("{prefix}…")
+    } else {
+        prefix
+    }
+}
+
+/// Which screen the single window is currently showing.
+#[derive(Default, PartialEq)]
+enum Screen {
+    #[default]
+    Menu,
+    Host,
+    Viewer,
+}
+
+/// Quality preset choices, mirroring `cli::Quality`. Map to the `--quality`
+/// argument value passed to the child.
+#[derive(Default, PartialEq, Clone, Copy)]
+enum QualitySel {
+    #[default]
+    Auto,
+    Source,
+    High,
+    Medium,
+    Low,
+}
+
+impl QualitySel {
+    fn as_arg(self) -> &'static str {
+        match self {
+            QualitySel::Auto => "auto",
+            QualitySel::Source => "source",
+            QualitySel::High => "high",
+            QualitySel::Medium => "medium",
+            QualitySel::Low => "low",
+        }
+    }
+
+    fn label(self) -> &'static str {
+        match self {
+            QualitySel::Auto => "Auto — pick from my upload speed",
+            QualitySel::Source => "Source — native resolution",
+            QualitySel::High => "High — up to 1080p",
+            QualitySel::Medium => "Medium — up to 720p",
+            QualitySel::Low => "Low — up to 480p",
+        }
+    }
+
+    const ALL: [QualitySel; 5] = [
+        QualitySel::Auto,
+        QualitySel::Source,
+        QualitySel::High,
+        QualitySel::Medium,
+        QualitySel::Low,
+    ];
+}
+
+/// Player choices for the viewer screen.
+#[derive(Default, PartialEq, Clone, Copy)]
+enum PlayerSel {
+    #[default]
+    Mpv,
+    Vlc,
+}
+
+impl PlayerSel {
+    fn to_player(self) -> crate::interactive::Player {
+        match self {
+            PlayerSel::Mpv => crate::interactive::Player::Mpv,
+            PlayerSel::Vlc => crate::interactive::Player::Vlc,
+        }
+    }
+}
+
+/// Host-screen state: the config form fields plus, once started, the running
+/// child and the latest values parsed from its event stream.
+struct HostState {
+    // form
+    quality: QualitySel,
+    max_viewers: u32, // 0 = let the host auto-size from the bandwidth preflight
+    no_hwencode: bool,
+    window: bool,
+    // running session + accumulated live state
+    proc: Option<ChildProc>,
+    ticket: Option<String>,
+    info: Option<HostInfo>,
+    active: u32,
+    max: u32,
+    capturing: bool,
+    /// Whether the current ticket made it onto the clipboard (auto-copy on
+    /// arrival, or a manual Copy click). Drives the "✓ Copied" hint so the
+    /// user isn't left guessing whether to click Copy — the trap that had
+    /// people pasting a stale clipboard ticket.
+    copied: bool,
+    last_refusal: Option<String>,
+    error: Option<String>,
+    viewers: Vec<String>,
+    tray_icon: Option<tray_icon::TrayIcon>,
+}
+
+impl Default for HostState {
+    fn default() -> Self {
+        Self {
+            quality: QualitySel::default(),
+            max_viewers: 0,
+            no_hwencode: false,
+            window: false,
+            proc: None,
+            ticket: None,
+            info: None,
+            active: 0,
+            max: 0,
+            capturing: false,
+            copied: false,
+            last_refusal: None,
+            error: None,
+            viewers: Vec::new(),
+            tray_icon: None,
+        }
+    }
+}
+
+/// The host config summary echoed back by the child's `host_info` event.
+struct HostInfo {
+    display: String,
+    capture: String,
+    quality: String,
+    dimensions: String,
+    hw_encode: bool,
+    cap_source: String,
+}
+
+/// Viewer-screen state.
+#[derive(Default)]
+struct ViewerState {
+    ticket_input: String,
+    player: PlayerSel,
+    proc: Option<ChildProc>,
+    url: Option<String>,
+    launched: bool,
+    /// Short endpoint id we're dialing, decoded from the ticket at Connect.
+    /// Shown in the "Connecting to …" line so a dead host is identifiable.
+    connecting_to: Option<String>,
+    /// Set when the View screen opens so the code field grabs focus once
+    /// (cleared on use, so it doesn't steal focus every frame).
+    focus_ticket: bool,
+    error: Option<String>,
+}
+
+#[derive(Default)]
+struct PixelPassApp {
+    screen: Screen,
+    host: HostState,
+    viewer: ViewerState,
+}
+
+impl eframe::App for PixelPassApp {
+    // eframe 0.34 hands us the central-panel `ui` directly.
+    fn ui(&mut self, ui: &mut egui::Ui, _frame: &mut eframe::Frame) {
+        // Drain any pending child events before drawing this frame.
+        self.pump_host_events();
+        self.pump_viewer_events();
+
+        if let Ok(_event) = tray_icon::menu::MenuEvent::receiver().try_recv() {
+            // Only one menu item right now: "Stop Hosting"
+            self.stop_host();
+        }
+
+        match self.screen {
+            Screen::Menu => self.menu(ui),
+            Screen::Host => self.host(ui),
+            Screen::Viewer => self.viewer(ui),
+        }
+    }
+}
+
+impl PixelPassApp {
+    fn menu(&mut self, ui: &mut egui::Ui) {
+        ui.vertical_centered(|ui| {
+            ui.add_space(24.0);
+            ui.heading("PixelPass");
+            ui.label("P2P screen sharing");
+            ui.label(
+                egui::RichText::new(concat!("v", env!("CARGO_PKG_VERSION")))
+                    .small()
+                    .weak(),
+            );
+            ui.add_space(32.0);
+            if ui
+                .add_sized([260.0, 40.0], egui::Button::new("Host — share my screen"))
+                .clicked()
+            {
+                self.screen = Screen::Host;
+            }
+            ui.add_space(8.0);
+            if ui
+                .add_sized(
+                    [260.0, 40.0],
+                    egui::Button::new("View — watch someone's screen"),
+                )
+                .clicked()
+            {
+                self.screen = Screen::Viewer;
+                self.prefill_viewer_ticket();
+            }
+        });
+    }
+
+    // ── Host screen ──────────────────────────────────────────────────────
+
+    fn host(&mut self, ui: &mut egui::Ui) {
+        let running = self.host.proc.is_some();
+        ui.horizontal(|ui| {
+            // Leaving the host screen stops the session (Drop on the child).
+            if ui.button("← Menu").clicked() {
+                self.stop_host();
+                self.screen = Screen::Menu;
+            }
+            ui.heading("Host");
+        });
+        ui.separator();
+
+        if running {
+            self.host_running(ui);
+        } else {
+            self.host_form(ui);
+        }
+    }
+
+    fn host_form(&mut self, ui: &mut egui::Ui) {
+        if let Some(err) = &self.host.error {
+            ui.colored_label(egui::Color32::LIGHT_RED, err);
+            ui.add_space(8.0);
+        }
+
+        egui::Grid::new("host_form")
+            .num_columns(2)
+            .spacing([12.0, 10.0])
+            .show(ui, |ui| {
+                ui.label("Quality");
+                egui::ComboBox::from_id_salt("quality")
+                    .selected_text(self.host.quality.label())
+                    .show_ui(ui, |ui| {
+                        for q in QualitySel::ALL {
+                            ui.selectable_value(&mut self.host.quality, q, q.label());
+                        }
+                    });
+                ui.end_row();
+
+                ui.label("Max viewers");
+                ui.horizontal(|ui| {
+                    ui.add(egui::DragValue::new(&mut self.host.max_viewers).range(0..=16));
+                    if self.host.max_viewers == 0 {
+                        ui.label("(auto from upload speed)");
+                    }
+                });
+                ui.end_row();
+
+                ui.label("Options");
+                ui.vertical(|ui| {
+                    ui.checkbox(&mut self.host.window, "Share a single window");
+                    ui.checkbox(
+                        &mut self.host.no_hwencode,
+                        "Software encoding (no GPU / VAAPI)",
+                    );
+                });
+                ui.end_row();
+            });
+
+        ui.add_space(16.0);
+        if ui
+            .add_sized([160.0, 36.0], egui::Button::new("Start hosting"))
+            .clicked()
+        {
+            self.start_host(ui.ctx().clone());
+        }
+        ui.add_space(8.0);
+        ui.label(
+            egui::RichText::new(
+                "On Wayland a \"Share Screen?\" dialog appears when the first \
+                 viewer connects.",
+            )
+            .small()
+            .weak(),
+        );
+    }
+
+    fn host_running(&mut self, ui: &mut egui::Ui) {
+        if self.host.capturing {
+            ui.colored_label(egui::Color32::LIGHT_GREEN, "● Streaming");
+        } else if self.host.ticket.is_some() {
+            ui.colored_label(egui::Color32::YELLOW, "● Waiting for viewers…");
+        } else {
+            ui.label("Starting…");
+        }
+
+        ui.add_space(6.0);
+        ui.label(format!("Viewers: {} / {}", self.host.active, self.host.max));
+        if !self.host.viewers.is_empty() {
+            ui.add_space(4.0);
+            for id in &self.host.viewers.clone() {
+                ui.horizontal(|ui| {
+                    ui.label(format!("• {}", short_id(id)));
+                    if ui.button("Kick").clicked() {
+                        if let Some(p) = &mut self.host.proc {
+                            p.send_command(&format!("kick {id}"));
+                        }
+                    }
+                });
+            }
+        }
+
+        if let Some(info) = &self.host.info {
+            ui.label(
+                egui::RichText::new(format!("{} · {}", info.display, info.capture))
+                    .small()
+                    .weak(),
+            );
+            ui.label(
+                egui::RichText::new(format!(
+                    "{} · {} · {} · cap {}",
+                    info.quality,
+                    info.dimensions,
+                    if info.hw_encode {
+                        "HW encode"
+                    } else {
+                        "software encode"
+                    },
+                    info.cap_source
+                ))
+                .small()
+                .weak(),
+            );
+        }
+
+        ui.add_space(12.0);
+
+        if let Some(ticket) = self.host.ticket.clone() {
+            ui.label("Share this code with your viewer(s):");
+            if let Some(id) = ticket_endpoint_id(&ticket) {
+                // The viewer shows "Connecting to <id>…" with this same
+                // truncation, so the two ends can be eyeballed for a match.
+                ui.label(
+                    egui::RichText::new(format!("This host: endpoint {}", short_id(&id)))
+                        .small()
+                        .weak(),
+                );
+            }
+            ui.add_space(4.0);
+            egui::Frame::group(ui.style()).show(ui, |ui| {
+                ui.add(
+                    egui::Label::new(egui::RichText::new(&ticket).monospace().small())
+                        .wrap()
+                        .selectable(true),
+                );
+            });
+            ui.add_space(4.0);
+            ui.horizontal(|ui| {
+                if ui.button("📋 Copy code").clicked() {
+                    self.copy_to_clipboard(&ticket);
+                }
+                if self.host.copied {
+                    ui.colored_label(egui::Color32::LIGHT_GREEN, "✓ Copied to clipboard");
+                }
+            });
+            if !self.host.copied {
+                ui.label(
+                    egui::RichText::new(
+                        "Couldn't auto-copy — click Copy, or select the code above.",
+                    )
+                    .small()
+                    .weak(),
+                );
+            }
+        }
+
+        if let Some(reason) = &self.host.last_refusal {
+            ui.add_space(8.0);
+            ui.colored_label(
+                egui::Color32::from_rgb(220, 160, 60),
+                format!("⚠ {reason}"),
+            );
+        }
+
+        ui.add_space(16.0);
+        if ui
+            .add_sized([140.0, 36.0], egui::Button::new("Stop hosting"))
+            .clicked()
+        {
+            self.stop_host();
+        }
+    }
+
+    fn start_host(&mut self, ctx: egui::Context) {
+        self.host.error = None;
+        self.host.last_refusal = None;
+        self.host.ticket = None;
+        self.host.info = None;
+        self.host.active = 0;
+        self.host.max = 0;
+        self.host.capturing = false;
+        self.host.copied = false;
+
+        let mut args = vec![
+            "--host".to_string(),
+            "--output".to_string(),
+            "json".to_string(),
+            "--quality".to_string(),
+            self.host.quality.as_arg().to_string(),
+        ];
+        if self.host.max_viewers > 0 {
+            args.push("--max-viewers".to_string());
+            args.push(self.host.max_viewers.to_string());
+        }
+        if self.host.no_hwencode {
+            args.push("--no-hwencode".to_string());
+        }
+        if self.host.window {
+            args.push("--window".to_string());
+        }
+
+        match ChildProc::spawn(&args, ctx) {
+            Ok(p) => {
+                self.host.proc = Some(p);
+
+                #[cfg(target_os = "linux")]
+                if let Err(e) = gtk::init() {
+                    tracing::warn!("Failed to initialize GTK for system tray: {e}");
+                }
+
+                use tray_icon::{TrayIconBuilder, menu::{Menu, MenuItem}};
+                let menu = Menu::new();
+                let _ = menu.append(&MenuItem::new("Stop Hosting", true, None));
+                let icon = tray_icon::Icon::from_rgba(vec![255, 0, 0, 255], 1, 1).unwrap();
+                if let Ok(tray) = TrayIconBuilder::new()
+                    .with_title("PixelPass")
+                    .with_tooltip("PixelPass Screen Sharing")
+                    .with_icon(icon)
+                    .with_menu(Box::new(menu))
+                    .build()
+                {
+                    self.host.tray_icon = Some(tray);
+                }
+            }
+            Err(e) => self.host.error = Some(format!("Couldn't start host: {e}")),
+        }
+    }
+
+    fn stop_host(&mut self) {
+        // Dropping the ChildProc SIGINTs the child and reaps it.
+        self.host.proc = None;
+        self.host.capturing = false;
+        self.host.ticket = None;
+        self.host.copied = false;
+        self.host.viewers.clear();
+        self.host.tray_icon = None;
+    }
+
+    /// Drain the host child's event channel into state, and detect an
+    /// unexpected child exit (e.g. a failed dependency check) so it surfaces
+    /// in the form instead of leaving a dead "running" view.
+    fn pump_host_events(&mut self) {
+        let events: Vec<ChildEvent> = match &self.host.proc {
+            Some(p) => std::iter::from_fn(|| p.rx.try_recv().ok()).collect(),
+            None => return,
+        };
+        for ev in events {
+            self.apply_host_event(ev);
+        }
+
+        if let Some(p) = &mut self.host.proc
+            && !p.is_alive()
+        {
+            if self.host.ticket.is_none() {
+                let tail = p.stderr_tail();
+                self.host.error = Some(if tail.trim().is_empty() {
+                    "Host exited before it could start.".to_string()
+                } else {
+                    format!("Host exited before it could start:\n{tail}")
+                });
+            }
+            self.host.proc = None;
+            self.host.capturing = false;
+        }
+    }
+
+    fn apply_host_event(&mut self, ev: ChildEvent) {
+        match ev {
+            ChildEvent::Ticket { value } => {
+                // Auto-copy on arrival, mirroring the CLI/interactive host
+                // (which copies the ticket and prints "copied to your
+                // clipboard"). A failure here is non-fatal: the ticket stays
+                // visible for manual copy, and `copied` stays false so the UI
+                // doesn't falsely claim success.
+                self.host.copied = set_clipboard(&value);
+                self.host.ticket = Some(value);
+            }
+            ChildEvent::HostInfo {
+                display_server,
+                capture,
+                quality,
+                dimensions,
+                hw_encode,
+                max_viewers,
+                max_viewers_source,
+            } => {
+                self.host.max = max_viewers;
+                self.host.info = Some(HostInfo {
+                    display: display_server,
+                    capture,
+                    quality,
+                    dimensions,
+                    hw_encode,
+                    cap_source: max_viewers_source,
+                });
+            }
+            ChildEvent::ViewerJoined { id, active, max } => {
+                self.host.active = active;
+                self.host.max = max;
+                if !self.host.viewers.contains(&id) {
+                    self.host.viewers.push(id.clone());
+                    let _ = notify_rust::Notification::new()
+                        .summary("PixelPass Viewer Connected")
+                        .body(&format!("Viewer {} joined the stream.", short_id(&id)))
+                        .show();
+                }
+            }
+            ChildEvent::ViewerLeft { id, active, max } => {
+                self.host.active = active;
+                self.host.max = max;
+                self.host.viewers.retain(|v| v != &id);
+                let _ = notify_rust::Notification::new()
+                    .summary("PixelPass Viewer Disconnected")
+                    .body(&format!("Viewer {} left the stream.", short_id(&id)))
+                    .show();
+            }
+            ChildEvent::Capture { state } => {
+                self.host.capturing = matches!(state, child::CaptureState::Started);
+            }
+            ChildEvent::ViewerRefused { reason } => self.host.last_refusal = Some(reason),
+            ChildEvent::Connected { .. } => {} // viewer-side; not used on the host screen
+        }
+    }
+
+    /// Manual Copy-button handler: copy and reflect success in the UI, or
+    /// surface a clear error if the clipboard rejected it.
+    fn copy_to_clipboard(&mut self, text: &str) {
+        if set_clipboard(text) {
+            self.host.copied = true;
+            self.host.error = None;
+        } else {
+            self.host.copied = false;
+            self.host.error = Some(
+                "Couldn't write to the clipboard. Select the code above and copy it manually."
+                    .to_string(),
+            );
+        }
+    }
+
+    // ── Viewer screen ─────────────────────────────────────────────────────
+
+    fn viewer(&mut self, ui: &mut egui::Ui) {
+        let running = self.viewer.proc.is_some();
+        ui.horizontal(|ui| {
+            if ui.button("← Menu").clicked() {
+                self.stop_viewer();
+                self.screen = Screen::Menu;
+            }
+            ui.heading("View");
+        });
+        ui.separator();
+
+        if running {
+            self.viewer_running(ui);
+        } else {
+            self.viewer_form(ui);
+        }
+    }
+
+    fn viewer_form(&mut self, ui: &mut egui::Ui) {
+        if let Some(err) = &self.viewer.error {
+            ui.colored_label(egui::Color32::LIGHT_RED, err);
+            ui.add_space(8.0);
+        }
+
+        ui.label("Paste the share code you received:");
+        ui.add_space(4.0);
+        // A Paste button (read-side mirror of the host's Copy button — one
+        // click grabs the code the host just put on the clipboard) with the
+        // field filling the rest of the row. A single horizontal row, so it
+        // doesn't grab the panel's full height.
+        let ticket_resp = ui
+            .horizontal(|ui| {
+                if ui.button("📋 Paste").clicked()
+                    && let Some(text) = get_clipboard()
+                {
+                    self.viewer.ticket_input = text.trim().to_string();
+                }
+                ui.add(
+                    egui::TextEdit::singleline(&mut self.viewer.ticket_input)
+                        .desired_width(f32::INFINITY)
+                        .hint_text("endpoint…"),
+                )
+            })
+            .inner;
+        // Grab focus once on screen entry so the user can paste/type straight
+        // away without first clicking into the field.
+        if std::mem::take(&mut self.viewer.focus_ticket) {
+            ticket_resp.request_focus();
+        }
+        // Enter in the field connects (gated on a decodable code below).
+        let enter_pressed =
+            ticket_resp.lost_focus() && ui.input(|i| i.key_pressed(egui::Key::Enter));
+
+        // Decode the pasted code live: confirms it's a real ticket and shows
+        // which host it points at, so a stale clipboard paste is caught here
+        // instead of after the 15s connect timeout.
+        let trimmed = self.viewer.ticket_input.trim().to_string();
+        let decoded_id = ticket_endpoint_id(&trimmed);
+        if !trimmed.is_empty() {
+            ui.add_space(4.0);
+            match &decoded_id {
+                Some(id) => ui.colored_label(
+                    egui::Color32::LIGHT_GREEN,
+                    format!("→ endpoint {}", short_id(id)),
+                ),
+                None => ui.colored_label(
+                    egui::Color32::from_rgb(220, 160, 60),
+                    "⚠ This doesn't look like a share code.",
+                ),
+            };
+        }
+
+        ui.add_space(10.0);
+        ui.horizontal(|ui| {
+            ui.label("Player");
+            egui::ComboBox::from_id_salt("player")
+                .selected_text(match self.viewer.player {
+                    PlayerSel::Mpv => "mpv",
+                    PlayerSel::Vlc => "VLC",
+                })
+                .show_ui(ui, |ui| {
+                    ui.selectable_value(&mut self.viewer.player, PlayerSel::Mpv, "mpv");
+                    ui.selectable_value(&mut self.viewer.player, PlayerSel::Vlc, "VLC");
+                });
+        });
+
+        ui.add_space(16.0);
+        // Only dial a code that actually decodes — no point spawning a child to
+        // spend 15s timing out against garbage. Enter takes the same path.
+        let connect_clicked = ui
+            .add_enabled(
+                decoded_id.is_some(),
+                egui::Button::new("Connect").min_size(egui::vec2(140.0, 36.0)),
+            )
+            .on_disabled_hover_text("Paste a valid share code first.")
+            .clicked();
+        if decoded_id.is_some() && (connect_clicked || enter_pressed) {
+            self.start_viewer(ui.ctx().clone());
+        }
+    }
+
+    fn viewer_running(&mut self, ui: &mut egui::Ui) {
+        if self.viewer.launched {
+            ui.colored_label(egui::Color32::LIGHT_GREEN, "● Streaming");
+            ui.label("Player launched. Close it or disconnect to stop.");
+        } else if self.viewer.url.is_some() {
+            ui.label("Connected — launching player…");
+        } else {
+            let msg = match &self.viewer.connecting_to {
+                Some(id) => format!("● Connecting to {id}…"),
+                None => "● Connecting…".to_string(),
+            };
+            ui.colored_label(egui::Color32::YELLOW, msg);
+        }
+
+        ui.add_space(16.0);
+        if ui
+            .add_sized([140.0, 36.0], egui::Button::new("Disconnect"))
+            .clicked()
+        {
+            self.stop_viewer();
+        }
+    }
+
+    /// On entering the View screen, drop a clipboard ticket straight into the
+    /// field — the host's Copy button (and our auto-copy) usually leaves the
+    /// freshly-shared code right there. Guarded so it only fires when the field
+    /// is empty and the clipboard holds a *decodable* ticket, so stray
+    /// clipboard text never lands in the box; the live decode still shows the
+    /// id for the user to verify.
+    fn prefill_viewer_ticket(&mut self) {
+        if self.viewer.ticket_input.trim().is_empty()
+            && self.viewer.proc.is_none()
+            && let Some(text) = get_clipboard()
+            && ticket_endpoint_id(&text).is_some()
+        {
+            self.viewer.ticket_input = text.trim().to_string();
+        }
+        self.viewer.focus_ticket = true;
+    }
+
+    fn start_viewer(&mut self, ctx: egui::Context) {
+        self.viewer.error = None;
+        self.viewer.url = None;
+        self.viewer.launched = false;
+
+        let ticket = self.viewer.ticket_input.trim().to_string();
+        self.viewer.connecting_to = ticket_endpoint_id(&ticket).map(|id| short_id(&id));
+        let args = vec![ticket, "--output".to_string(), "json".to_string()];
+        match ChildProc::spawn(&args, ctx) {
+            Ok(p) => self.viewer.proc = Some(p),
+            Err(e) => self.viewer.error = Some(format!("Couldn't connect: {e}")),
+        }
+    }
+
+    fn stop_viewer(&mut self) {
+        self.viewer.proc = None;
+        self.viewer.url = None;
+        self.viewer.launched = false;
+        self.viewer.connecting_to = None;
+    }
+
+    fn pump_viewer_events(&mut self) {
+        let events: Vec<ChildEvent> = match &self.viewer.proc {
+            Some(p) => std::iter::from_fn(|| p.rx.try_recv().ok()).collect(),
+            None => return,
+        };
+        for ev in events {
+            if let ChildEvent::Connected { url } = ev {
+                self.viewer.url = Some(url.clone());
+                if !self.viewer.launched {
+                    match self.viewer.player.to_player().spawn(&url) {
+                        Ok(()) => self.viewer.launched = true,
+                        Err(e) => self.viewer.error = Some(format!("Couldn't launch player: {e}")),
+                    }
+                }
+            }
+        }
+
+        if let Some(p) = &mut self.viewer.proc
+            && !p.is_alive()
+        {
+            // Bridge ended (player closed) or the connection failed.
+            if self.viewer.url.is_none() {
+                let tail = p.stderr_tail();
+                self.viewer.error = Some(if tail.trim().is_empty() {
+                    "Couldn't connect to the host (check the code).".to_string()
+                } else {
+                    format!("Connection ended:\n{tail}")
+                });
+            }
+            self.viewer.proc = None;
+            self.viewer.launched = false;
+            self.viewer.url = None;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// A real, parseable ticket built the same way the host builds one
+    /// (`EndpointTicket::new`), from a deterministic key so the id is stable.
+    fn sample_ticket() -> (String, String) {
+        let sk = iroh::SecretKey::from_bytes(&[7u8; 32]);
+        let id = sk.public().to_string();
+        let ticket = iroh_tickets::endpoint::EndpointTicket::new(iroh::EndpointAddr::new(
+            sk.public(),
+        ))
+        .to_string();
+        (ticket, id)
+    }
+
+    #[test]
+    fn decodes_endpoint_id_from_a_valid_ticket() {
+        let (ticket, id) = sample_ticket();
+        assert_eq!(ticket_endpoint_id(&ticket).as_deref(), Some(id.as_str()));
+    }
+
+    #[test]
+    fn tolerates_surrounding_whitespace() {
+        let (ticket, _) = sample_ticket();
+        assert!(ticket_endpoint_id(&format!("  \n{ticket}\t ")).is_some());
+    }
+
+    #[test]
+    fn rejects_non_ticket_input() {
+        // The empty/whitespace/garbage cases that gate the Connect button off.
+        assert_eq!(ticket_endpoint_id(""), None);
+        assert_eq!(ticket_endpoint_id("   "), None);
+        assert_eq!(ticket_endpoint_id("hello world"), None);
+        assert_eq!(ticket_endpoint_id("endpointbutnotreally"), None);
+    }
+
+    #[test]
+    fn short_id_truncates_long_ids() {
+        assert_eq!(short_id("0123456789abcdefghij"), "0123456789ab…");
+    }
+
+    #[test]
+    fn short_id_leaves_short_or_exact_ids_intact() {
+        assert_eq!(short_id("abc"), "abc");
+        assert_eq!(short_id("0123456789ab"), "0123456789ab"); // exactly 12, no ellipsis
+    }
+}

src/host/audio.rs

@@ -0,0 +1,539 @@
+//! Per-app audio routing.
+//!
+//! Two cooperating layers:
+//!
+//! - **Null-sink + loopback** (pactl shell-out): a per-PID null-sink
+//!   `pixelpass_capture_<pid>` plus a `module-loopback` that mirrors the
+//!   default sink's monitor into it. gst captures from the null-sink's
+//!   monitor, so the viewer hears whatever the user hears — by default.
+//!
+//! - **Per-stream rerouting** (libpipewire on a dedicated OS thread):
+//!   when [`HostOpts::app`] is set, a [`StreamRouter`] subscribes to the
+//!   PipeWire registry, finds `Stream/Output/Audio` nodes whose
+//!   `application.name` matches the filter, and writes
+//!   `target.object` to the "default" metadata so WirePlumber reroutes
+//!   them to our null-sink. Once at least one stream is actually routed,
+//!   the loopback is unloaded — otherwise the viewer would hear the
+//!   filtered audio twice (once via the routed stream, once via the
+//!   default-sink monitor loopback).
+//!
+//! pactl is the right tool for the one-shot null-sink/loopback graph
+//! mutations. libpipewire is dragged in only when per-stream filtering
+//! is requested, because that needs registry-event subscription.
+
+use anyhow::{Context, Result, bail};
+use std::cell::RefCell;
+use std::collections::BTreeMap;
+use std::process::Command;
+use std::rc::Rc;
+use std::sync::{Arc, Mutex};
+use std::thread::JoinHandle;
+
+use crate::cli::HostOpts;
+
+/// Owns the pactl-loaded modules plus, when filtering is active, the
+/// libpipewire stream-router thread. Drop unloads modules as a backstop;
+/// prefer [`Routing::shutdown`] explicitly so failures get logged.
+pub struct Routing {
+    sink_module: Option<u32>,
+    /// Shared with the event task so it can `take()` and unload on the
+    /// first successful route. `Routing::shutdown` unloads whatever
+    /// remains.
+    loopback_module: Arc<Mutex<Option<u32>>>,
+    sink_name: String,
+    stream_router: Option<StreamRouter>,
+    event_task: Option<tokio::task::JoinHandle<()>>,
+}
+
+impl Routing {
+    /// Create the per-PID null-sink + loopback. If `opts.app` is set,
+    /// also spawn the libpipewire thread that reroutes matching streams.
+    pub async fn start(opts: &HostOpts) -> Result<Self> {
+        let pid = std::process::id();
+        let sink_name = format!("pixelpass_capture_{pid}");
+
+        let sink_module =
+            load_module(&["module-null-sink", &format!("sink_name={sink_name}")])
+                .context("failed to load module-null-sink")?;
+
+        // 20ms loopback latency keeps the mirrored audio tight; pactl's
+        // default of 200ms is enough to be perceptible.
+        let loopback_module = load_module(&[
+            "module-loopback",
+            "source=@DEFAULT_SINK@.monitor",
+            &format!("sink={sink_name}"),
+            "latency_msec=20",
+        ])
+        .context("failed to load module-loopback (null-sink will be cleaned up on Drop)")?;
+
+        tracing::info!(
+            sink_module,
+            loopback_module,
+            %sink_name,
+            "audio routing: null-sink + loopback ready"
+        );
+
+        let loopback_arc = Arc::new(Mutex::new(Some(loopback_module)));
+        let mut routing = Self {
+            sink_module: Some(sink_module),
+            loopback_module: Arc::clone(&loopback_arc),
+            sink_name: sink_name.clone(),
+            stream_router: None,
+            event_task: None,
+        };
+
+        if let Some(app) = &opts.app {
+            let (router, mut event_rx) = StreamRouter::spawn(app.clone(), sink_name.clone())?;
+            let loopback_for_task = Arc::clone(&loopback_arc);
+            let sink_name_for_task = sink_name.clone();
+            let event_task = tokio::spawn(async move {
+                while let Some(ev) = event_rx.recv().await {
+                    match ev {
+                        Event::FirstRoutedStream => {
+                            let mid = loopback_for_task.lock().unwrap().take();
+                            if let Some(id) = mid {
+                                tracing::info!(
+                                    "audio routing: first stream routed → unloading default-sink loopback"
+                                );
+                                unload_module(id);
+                            }
+                        }
+                        Event::LastRoutedStreamGone => {
+                            // Routed app exited mid-session. Restore the
+                            // default-sink loopback so the viewer hears
+                            // system audio again instead of silence.
+                            if loopback_for_task.lock().unwrap().is_some() {
+                                continue;
+                            }
+                            tracing::info!(
+                                "audio routing: last routed stream gone → restoring default-sink loopback"
+                            );
+                            match load_module(&[
+                                "module-loopback",
+                                "source=@DEFAULT_SINK@.monitor",
+                                &format!("sink={sink_name_for_task}"),
+                                "latency_msec=20",
+                            ]) {
+                                Ok(id) => {
+                                    *loopback_for_task.lock().unwrap() = Some(id);
+                                }
+                                Err(e) => {
+                                    tracing::warn!(
+                                        "audio routing: failed to re-load loopback: {e:#}"
+                                    );
+                                }
+                            }
+                        }
+                    }
+                }
+            });
+            routing.stream_router = Some(router);
+            routing.event_task = Some(event_task);
+        }
+
+        Ok(routing)
+    }
+
+    pub fn sink_name(&self) -> &str {
+        &self.sink_name
+    }
+
+    /// Stop the stream router (if any), then unload loopback (if still
+    /// loaded), then unload the null-sink. Order matters: PipeWire can
+    /// leave zombie links if you destroy a sink with active inputs.
+    pub fn shutdown(mut self) {
+        if let Some(router) = self.stream_router.take() {
+            router.shutdown();
+        }
+        if let Some(task) = self.event_task.take() {
+            task.abort();
+        }
+        if let Some(id) = self.loopback_module.lock().unwrap().take() {
+            unload_module(id);
+        }
+        if let Some(id) = self.sink_module.take() {
+            unload_module(id);
+        }
+    }
+}
+
+impl Drop for Routing {
+    fn drop(&mut self) {
+        if let Some(router) = self.stream_router.take() {
+            router.shutdown();
+        }
+        if let Some(task) = self.event_task.take() {
+            task.abort();
+        }
+        if let Some(id) = self.loopback_module.lock().unwrap().take() {
+            unload_module(id);
+        }
+        if let Some(id) = self.sink_module.take() {
+            unload_module(id);
+        }
+    }
+}
+
+// ──────────────────────────────────────────────────────────────────────
+// App enumeration (interactive picker source)
+// ──────────────────────────────────────────────────────────────────────
+
+/// One deduplicated app currently producing audio. The picker in
+/// interactive mode shows these as the per-app capture choices.
+#[derive(Debug, Clone)]
+pub struct App {
+    pub name: String,
+    pub stream_count: u32,
+}
+
+/// Enumerate apps currently sending audio to any sink, deduplicated by
+/// `application.name`. Returns an empty Vec if nothing is playing.
+pub fn list_playing_apps() -> Result<Vec<App>> {
+    let output = Command::new("pactl")
+        .args(["-f", "json", "list", "sink-inputs"])
+        .output()
+        .context("failed to run `pactl -f json list sink-inputs`")?;
+    if !output.status.success() {
+        bail!(
+            "pactl list sink-inputs failed: {}",
+            String::from_utf8_lossy(&output.stderr).trim()
+        );
+    }
+    parse_sink_inputs(&output.stdout)
+}
+
+fn parse_sink_inputs(stdout: &[u8]) -> Result<Vec<App>> {
+    let entries: Vec<SinkInput> =
+        serde_json::from_slice(stdout).context("pactl returned unparseable JSON")?;
+    let mut counts: BTreeMap<String, u32> = BTreeMap::new();
+    for entry in entries {
+        let Some(name) = entry.properties.application_name else { continue };
+        let trimmed = name.trim();
+        if trimmed.is_empty() {
+            continue;
+        }
+        *counts.entry(trimmed.to_string()).or_insert(0) += 1;
+    }
+    Ok(counts
+        .into_iter()
+        .map(|(name, stream_count)| App { name, stream_count })
+        .collect())
+}
+
+#[derive(serde::Deserialize)]
+struct SinkInput {
+    properties: SinkInputProperties,
+}
+
+#[derive(serde::Deserialize)]
+struct SinkInputProperties {
+    #[serde(rename = "application.name")]
+    application_name: Option<String>,
+}
+
+// ──────────────────────────────────────────────────────────────────────
+// pactl module helpers
+// ──────────────────────────────────────────────────────────────────────
+
+fn load_module(args: &[&str]) -> Result<u32> {
+    let output = Command::new("pactl")
+        .arg("load-module")
+        .args(args)
+        .output()
+        .context("failed to run pactl load-module")?;
+    if !output.status.success() {
+        bail!(
+            "pactl load-module failed: {}",
+            String::from_utf8_lossy(&output.stderr).trim()
+        );
+    }
+    let id_str = String::from_utf8(output.stdout)
+        .context("pactl returned non-UTF-8")?
+        .trim()
+        .to_string();
+    id_str
+        .parse::<u32>()
+        .with_context(|| format!("pactl returned unexpected module ID: {id_str:?}"))
+}
+
+fn unload_module(id: u32) {
+    let result = Command::new("pactl")
+        .arg("unload-module")
+        .arg(id.to_string())
+        .output();
+    match result {
+        Ok(output) if output.status.success() => {
+            tracing::info!(module = id, "audio routing: unloaded pactl module");
+        }
+        Ok(output) => {
+            tracing::warn!(
+                module = id,
+                stderr = %String::from_utf8_lossy(&output.stderr).trim(),
+                "audio routing: pactl unload-module exited non-zero"
+            );
+        }
+        Err(e) => {
+            tracing::warn!(
+                module = id,
+                "audio routing: failed to run pactl unload-module: {e}"
+            );
+        }
+    }
+}
+
+// ──────────────────────────────────────────────────────────────────────
+// Per-stream routing (libpipewire thread)
+// ──────────────────────────────────────────────────────────────────────
+
+/// Command from tokio → libpipewire thread.
+enum Cmd {
+    /// Clear `target.object` for everything we routed, then quit the
+    /// MainLoop so the thread joins.
+    Shutdown,
+}
+
+/// Event from libpipewire thread → tokio. The pair drives loopback
+/// oscillation: unload on `FirstRoutedStream`, re-load on
+/// `LastRoutedStreamGone`. Both fire on count-transitions (0→N and N→0
+/// respectively), not on every change.
+enum Event {
+    /// At least one stream is now routed to our sink. Receiver unloads
+    /// the default-sink loopback so the filtered audio isn't doubled.
+    FirstRoutedStream,
+    /// The last routed stream just disappeared (app closed, paused,
+    /// switched output). Receiver re-loads the default-sink loopback so
+    /// the viewer doesn't go silent.
+    LastRoutedStreamGone,
+}
+
+/// Handle to the libpipewire stream-router thread.
+pub struct StreamRouter {
+    cmd_tx: pipewire::channel::Sender<Cmd>,
+    thread: Option<JoinHandle<()>>,
+}
+
+impl StreamRouter {
+    /// Spawn the libpipewire thread. Returns the router handle and the
+    /// event receiver tokio side polls.
+    fn spawn(
+        filter_name: String,
+        sink_name: String,
+    ) -> Result<(Self, tokio::sync::mpsc::UnboundedReceiver<Event>)> {
+        let (cmd_tx, cmd_rx) = pipewire::channel::channel::<Cmd>();
+        let (event_tx, event_rx) = tokio::sync::mpsc::unbounded_channel::<Event>();
+
+        let thread = std::thread::Builder::new()
+            .name("pixelpass-pw-router".to_string())
+            .spawn(move || {
+                if let Err(e) = run_router(filter_name, sink_name, cmd_rx, event_tx) {
+                    tracing::warn!("audio routing: libpipewire thread exited with error: {e:#}");
+                }
+            })
+            .context("failed to spawn libpipewire router thread")?;
+
+        Ok((
+            Self {
+                cmd_tx,
+                thread: Some(thread),
+            },
+            event_rx,
+        ))
+    }
+
+    fn shutdown(mut self) {
+        // Best-effort: if the send fails the thread is already gone.
+        let _ = self.cmd_tx.send(Cmd::Shutdown);
+        if let Some(t) = self.thread.take()
+            && let Err(e) = t.join()
+        {
+            tracing::warn!("audio routing: pw thread join failed: {e:?}");
+        }
+    }
+}
+
+/// Body of the libpipewire thread. Owns MainLoop, registry listener, and
+/// all PipeWire proxies for the duration of the routing session.
+fn run_router(
+    filter_name: String,
+    sink_name: String,
+    cmd_rx: pipewire::channel::Receiver<Cmd>,
+    event_tx: tokio::sync::mpsc::UnboundedSender<Event>,
+) -> Result<()> {
+    use pipewire::{self as pw, types::ObjectType};
+
+    let main_loop = pw::main_loop::MainLoopRc::new(None)
+        .context("pw main loop construction failed")?;
+    let context = pw::context::ContextRc::new(&main_loop, None)
+        .context("pw context construction failed")?;
+    let core = context
+        .connect_rc(None)
+        .context("pw core connect failed (is the daemon running?)")?;
+    let registry = core
+        .get_registry_rc()
+        .context("pw get_registry failed")?;
+
+    let state = Rc::new(RefCell::new(RouterState {
+        sink_serial: None,
+        default_metadata: None,
+        routed_node_ids: Vec::new(),
+        pending: Vec::new(),
+    }));
+
+    // Cmd handler: clear metadata for routed streams, then quit.
+    let main_loop_for_cmd = main_loop.clone();
+    let state_for_cmd = Rc::clone(&state);
+    let _cmd_recv = cmd_rx.attach(main_loop.loop_(), move |cmd| match cmd {
+        Cmd::Shutdown => {
+            let s = state_for_cmd.borrow();
+            if let Some(meta) = &s.default_metadata {
+                for &nid in &s.routed_node_ids {
+                    meta.set_property(nid, "target.object", None, None);
+                }
+                if !s.routed_node_ids.is_empty() {
+                    tracing::info!(
+                        n = s.routed_node_ids.len(),
+                        "audio routing: cleared target.object on routed streams before quitting"
+                    );
+                }
+            }
+            main_loop_for_cmd.quit();
+        }
+    });
+
+    let filter_lower = filter_name.to_ascii_lowercase();
+    let sink_name_owned = sink_name.clone();
+    let registry_weak = registry.downgrade();
+    let state_for_reg = Rc::clone(&state);
+    let event_tx_for_reg = event_tx.clone();
+    let state_for_remove = Rc::clone(&state);
+    let event_tx_for_remove = event_tx.clone();
+
+    let _reg_listener = registry
+        .add_listener_local()
+        .global(move |obj| {
+            let Some(reg) = registry_weak.upgrade() else { return };
+            match obj.type_ {
+                ObjectType::Node => {
+                    let Some(props) = obj.props.as_ref() else { return };
+                    if props.get("node.name") == Some(sink_name_owned.as_str()) {
+                        if let Some(serial) = props
+                            .get("object.serial")
+                            .and_then(|s| s.parse::<u32>().ok())
+                        {
+                            state_for_reg.borrow_mut().sink_serial = Some(serial);
+                            tracing::info!(
+                                serial,
+                                "audio routing: pixelpass sink registered"
+                            );
+                            try_flush(&state_for_reg, &event_tx_for_reg);
+                        }
+                        return;
+                    }
+                    if props.get("media.class") != Some("Stream/Output/Audio") {
+                        return;
+                    }
+                    let Some(app) = props.get("application.name") else { return };
+                    if !app.eq_ignore_ascii_case(&filter_lower) {
+                        return;
+                    }
+                    tracing::info!(
+                        node_id = obj.id,
+                        %app,
+                        "audio routing: matched stream, queued for route"
+                    );
+                    state_for_reg.borrow_mut().pending.push(obj.id);
+                    try_flush(&state_for_reg, &event_tx_for_reg);
+                }
+                ObjectType::Metadata => {
+                    let Some(props) = obj.props.as_ref() else { return };
+                    if props.get("metadata.name") != Some("default") {
+                        return;
+                    }
+                    let metadata: pw::metadata::Metadata = match reg.bind(obj) {
+                        Ok(m) => m,
+                        Err(e) => {
+                            tracing::warn!("audio routing: bind default metadata failed: {e}");
+                            return;
+                        }
+                    };
+                    state_for_reg.borrow_mut().default_metadata = Some(metadata);
+                    tracing::info!("audio routing: default metadata bound");
+                    try_flush(&state_for_reg, &event_tx_for_reg);
+                }
+                _ => {}
+            }
+        })
+        .global_remove(move |id| {
+            handle_global_remove(&state_for_remove, &event_tx_for_remove, id);
+        })
+        .register();
+
+    tracing::info!(filter = %filter_name, "audio routing: pw thread running");
+    main_loop.run();
+    tracing::info!("audio routing: pw thread exiting");
+    Ok(())
+}
+
+struct RouterState {
+    sink_serial: Option<u32>,
+    default_metadata: Option<pipewire::metadata::Metadata>,
+    routed_node_ids: Vec<u32>,
+    pending: Vec<u32>,
+}
+
+/// Drop the vanished node from `routed_node_ids` and `pending`. If it
+/// was the last routed stream, emit `LastRoutedStreamGone` so the
+/// tokio side restores the default-sink loopback.
+fn handle_global_remove(
+    state: &Rc<RefCell<RouterState>>,
+    event_tx: &tokio::sync::mpsc::UnboundedSender<Event>,
+    id: u32,
+) {
+    let mut s = state.borrow_mut();
+    let was_routed = !s.routed_node_ids.is_empty();
+    s.routed_node_ids.retain(|&x| x != id);
+    s.pending.retain(|&x| x != id);
+    if was_routed && s.routed_node_ids.is_empty() {
+        tracing::info!(
+            node_id = id,
+            "audio routing: last routed stream disappeared"
+        );
+        let _ = event_tx.send(Event::LastRoutedStreamGone);
+    }
+}
+
+/// Drain pending streams to the sink, but only once both prerequisites
+/// (sink serial known + default metadata bound) are in place. Emits
+/// `FirstRoutedStream` when routed count crosses 0→N (so it fires
+/// each time the count comes back up from zero, not just the first
+/// time — pairs with `LastRoutedStreamGone` to oscillate the loopback).
+fn try_flush(
+    state: &Rc<RefCell<RouterState>>,
+    event_tx: &tokio::sync::mpsc::UnboundedSender<Event>,
+) {
+    let mut s = state.borrow_mut();
+    let Some(serial) = s.sink_serial else { return };
+    if s.default_metadata.is_none() {
+        return;
+    }
+    if s.pending.is_empty() {
+        return;
+    }
+    let was_empty = s.routed_node_ids.is_empty();
+    let serial_str = serial.to_string();
+    let pending = std::mem::take(&mut s.pending);
+    if let Some(meta) = &s.default_metadata {
+        for nid in &pending {
+            meta.set_property(*nid, "target.object", Some("Spa:Id"), Some(&serial_str));
+            tracing::info!(
+                node_id = *nid,
+                sink_serial = serial,
+                "audio routing: stream routed to pixelpass sink"
+            );
+        }
+    }
+    s.routed_node_ids.extend(pending);
+    if was_empty && !s.routed_node_ids.is_empty() {
+        let _ = event_tx.send(Event::FirstRoutedStream);
+    }
+}

src/host/capture.rs

@@ -1,40 +1,25 @@
-//! Capture dispatcher. Selects the per-display-server pipeline and returns its
-//! [`CaptureHandle`]. Each backend owns its own children and tears them down
-//! via its own Drop / shutdown.
+//! Capture dispatcher. Picks the per-display-server source backend and returns
+//! the shared [`pipeline::CaptureHandle`]. The handle itself, its teardown, and
+//! the whole encode/serve tail are display-agnostic and live in
+//! [`super::pipeline`]; the backends differ only in how they obtain a video
+//! source element.
 
-use anyhow::{Result, bail};
+use anyhow::Result;
 
 use crate::cli::HostOpts;
 use crate::common::display::DisplayServer;
-use crate::host::wayland;
+use crate::host::pipeline::CaptureHandle;
+use crate::host::quality::EffectiveQuality;
+use crate::host::{wayland, x11};
 
-pub enum CaptureHandle {
-    Wayland(wayland::CaptureHandle),
-}
-
-impl CaptureHandle {
-    pub fn local_port(&self) -> u16 {
-        match self {
-            CaptureHandle::Wayland(h) => h.local_port(),
-        }
-    }
-
-    pub async fn shutdown(self) {
-        match self {
-            CaptureHandle::Wayland(h) => h.shutdown().await,
-        }
-    }
-}
-
-pub async fn spawn(display: DisplayServer, opts: &HostOpts) -> Result<CaptureHandle> {
+pub async fn spawn(
+    display: DisplayServer,
+    opts: &HostOpts,
+    quality: &EffectiveQuality,
+) -> Result<CaptureHandle> {
     match display {
-        DisplayServer::Wayland => {
-            let h = wayland::start(opts).await?;
-            Ok(CaptureHandle::Wayland(h))
-        }
-        DisplayServer::X11 => {
-            bail!("X11 capture pipeline not yet implemented (Phase 2 follow-up)");
-        }
+        DisplayServer::Wayland => wayland::start(opts, quality).await,
+        DisplayServer::X11 => x11::start(opts, quality).await,
         DisplayServer::Unknown => unreachable!("caller guarantees display != Unknown"),
     }
 }

src/host/mod.rs

@@ -1,18 +1,50 @@
+pub mod audio;
 mod capture;
+mod pipeline;
+mod quality;
+mod serve;
 mod wayland;
+mod x11;
 
 use anyhow::{Result, bail};
-use iroh::Endpoint;
 use iroh::endpoint::{Connection, presets};
+use iroh::{Endpoint, EndpointAddr};
 use iroh_tickets::endpoint::EndpointTicket;
+use std::collections::HashMap;
+use std::time::Duration;
+use tokio::io::{AsyncBufReadExt, BufReader};
+use tokio::sync::{mpsc, oneshot};
 use tokio_util::sync::CancellationToken;
 
 use crate::cli::HostOpts;
-use crate::common::{alpn::ALPN, deps, display::DisplayServer, signal};
+use crate::common::{
+    alpn::ALPN, bandwidth, config, config::BandwidthStatus, deps, display::DisplayServer, output,
+    signal, tunnel,
+};
+
+use self::pipeline::CaptureHandle;
+use self::quality::EffectiveQuality;
+
+/// Messages from per-viewer tasks to the capture supervisor.
+enum SupervisorMsg {
+    /// A new viewer wants in. Supervisor replies with the local capture
+    /// HTTP port to connect to, or an error string if the host is full or
+    /// capture spawn failed.
+    AddViewer {
+        id: String,
+        cancel: CancellationToken,
+        reply: oneshot::Sender<Result<u16, String>>,
+    },
+    /// A viewer's session ended. Supervisor decrements the count and tears
+    /// down capture if it just hit zero.
+    RemoveViewer { id: String },
+    /// Request to kick a specific viewer.
+    KickViewer { id: String },
+}
 
 pub async fn run(opts: HostOpts) -> Result<()> {
     let display = DisplayServer::resolve(opts.display_server);
-    deps::check_host_binaries(display)?;
+    deps::check_host_binaries(display, &opts)?;
 
     if display == DisplayServer::Unknown {
         bail!(
@@ -21,6 +53,19 @@ pub async fn run(opts: HostOpts) -> Result<()> {
         );
     }
 
+    // Resolve quality first: Auto sizes its bandwidth budget against the viewer
+    // cap the host will honor. To avoid a circular dependency (the auto-derived
+    // cap itself depends on bitrate), Auto sizes against the user's explicit
+    // --max-viewers when given, else a single viewer. The resulting effective
+    // bitrate then feeds the cap resolution below.
+    let sizing_viewers = opts.max_viewers.filter(|&n| n > 0).unwrap_or(1);
+    let quality = quality::resolve(&opts, sizing_viewers);
+
+    let resolution = resolve_max_viewers(&opts, quality.bitrate);
+    if resolution.value == 0 {
+        bail!("--max-viewers must be at least 1");
+    }
+
     let cancel = signal::install_ctrl_c();
 
     let endpoint = Endpoint::builder(presets::N0)
@@ -28,101 +73,340 @@ pub async fn run(opts: HostOpts) -> Result<()> {
         .bind()
         .await?;
 
+    // Relay-only ticket: wait for the home relay to connect, then keep only
+    // the endpoint id + relay URL and drop the direct IP candidates. The relay
+    // coordinates hole-punching to a direct path right after connect, so this
+    // doesn't change whether peers can reach each other — it just keeps the
+    // ticket short (~140 vs ~320 chars) and stops it from leaking LAN /
+    // Docker-bridge addresses to whoever receives the ticket. Awaiting online()
+    // first guarantees the relay URL is actually present (addr() right after
+    // bind can return before the relay handshake completes); the 15s cap means
+    // a relay outage degrades to a possibly-incomplete ticket rather than a hang
+    // (n0 DNS discovery still resolves the id in that case).
+    if tokio::time::timeout(Duration::from_secs(15), endpoint.online())
+        .await
+        .is_err()
+    {
+        tracing::warn!("home relay not connected within 15s; ticket may be incomplete");
+    }
     let addr = endpoint.addr();
-    let ticket = EndpointTicket::new(addr);
-    let clipboard_ok = opts.interactive && copy_to_clipboard(&ticket.to_string());
-    print_host_banner(&ticket, display, &opts, clipboard_ok);
+    let relay_only =
+        EndpointAddr::new(addr.id).with_addrs(addr.addrs.iter().filter(|a| a.is_relay()).cloned());
+    let ticket = EndpointTicket::new(relay_only);
+    let ticket_str = ticket.to_string();
+    let clipboard_ok = opts.interactive && copy_to_clipboard(&ticket_str);
+    print_host_banner(&ticket, display, &opts, &quality, &resolution, clipboard_ok);
 
-    let result = accept_loop(&endpoint, display, &opts, cancel.clone()).await;
+    output::emit(output::Event::Ticket { value: &ticket_str });
+    let display_str = format!("{display:?}");
+    let capture = capture_summary(&opts);
+    let dims = quality.dimensions_summary();
+    let cap_source = resolution.source.label();
+    output::emit(output::Event::HostInfo {
+        display_server: &display_str,
+        capture: &capture,
+        quality: &quality.label,
+        dimensions: &dims,
+        hw_encode: !opts.no_hwencode,
+        max_viewers: resolution.value,
+        max_viewers_source: &cap_source,
+    });
+
+    let (sup_tx, sup_rx) = mpsc::channel::<SupervisorMsg>(16);
+    let supervisor = tokio::spawn(supervise(
+        opts.clone(),
+        quality,
+        display,
+        resolution.value,
+        sup_rx,
+    ));
+
+    // Stdin listener for "kick <id>"
+    let stdin_sup_tx = sup_tx.clone();
+    tokio::spawn(async move {
+        let mut lines = BufReader::new(tokio::io::stdin()).lines();
+        while let Ok(Some(line)) = lines.next_line().await {
+            if let Some(id) = line.strip_prefix("kick ") {
+                let _ = stdin_sup_tx.send(SupervisorMsg::KickViewer { id: id.trim().to_string() }).await;
+            }
+        }
+    });
+
+    accept_loop(&endpoint, sup_tx.clone(), cancel.clone()).await;
+
+    drop(sup_tx);
+    let _ = supervisor.await;
 
     endpoint.close().await;
-    result
+    Ok(())
 }
 
 async fn accept_loop(
     endpoint: &Endpoint,
-    display: DisplayServer,
-    opts: &HostOpts,
+    sup_tx: mpsc::Sender<SupervisorMsg>,
     cancel: CancellationToken,
-) -> Result<()> {
-    tokio::select! {
-        _ = cancel.cancelled() => {
-            tracing::info!("cancellation requested before any peer connected");
-            Ok(())
-        }
-        accepted = endpoint.accept() => {
-            let Some(incoming) = accepted else {
-                bail!("endpoint stopped accepting connections");
-            };
-            let conn = incoming.await?;
-            let remote = conn.remote_id();
-            tracing::info!(%remote, "peer connected");
-            eprintln!("\n[pixelpass] peer connected: {remote}\n");
-            handle_peer(conn, display, opts, cancel).await
+) {
+    loop {
+        tokio::select! {
+            _ = cancel.cancelled() => {
+                tracing::info!("cancellation requested — closing accept loop");
+                return;
+            }
+            accepted = endpoint.accept() => {
+                let Some(incoming) = accepted else {
+                    tracing::info!("endpoint stopped accepting connections");
+                    return;
+                };
+                let conn = match incoming.await {
+                    Ok(c) => c,
+                    Err(e) => {
+                        tracing::warn!("incoming connection failed: {e:#}");
+                        continue;
+                    }
+                };
+                let sup_tx = sup_tx.clone();
+                let cancel = cancel.clone();
+                tokio::spawn(handle_peer(conn, sup_tx, cancel));
+            }
         }
     }
 }
 
 async fn handle_peer(
     conn: Connection,
-    display: DisplayServer,
-    opts: &HostOpts,
+    sup_tx: mpsc::Sender<SupervisorMsg>,
     cancel: CancellationToken,
-) -> Result<()> {
-    let (quic_send, quic_recv) = conn.accept_bi().await?;
+) {
+    let remote = conn.remote_id();
+    let id_str = remote.to_string();
+    let peer_cancel = CancellationToken::new();
 
-    let capture_handle = capture::spawn(display, opts).await?;
-    let port = capture_handle.local_port();
-    let tcp = wayland::connect_to_capture(port, std::time::Duration::from_secs(5)).await?;
-
-    let bridge = crate::common::tunnel::bridge(quic_send, quic_recv, tcp);
-
-    tokio::select! {
-        res = bridge => {
-            if let Err(e) = res {
-                tracing::warn!("bridge ended with error: {e:#}");
-            } else {
-                tracing::info!("bridge closed cleanly");
-            }
+    let (reply_tx, reply_rx) = oneshot::channel();
+    if sup_tx.send(SupervisorMsg::AddViewer { id: id_str.clone(), cancel: peer_cancel.clone(), reply: reply_tx }).await.is_err() {
+        tracing::warn!(%remote, "supervisor channel closed; dropping peer");
+        return;
+    }
+    let port = match reply_rx.await {
+        Ok(Ok(p)) => p,
+        Ok(Err(reason)) => {
+            tracing::warn!(%remote, %reason, "refusing viewer");
+            eprintln!("[pixelpass] refusing viewer {remote}: {reason}");
+            return;
         }
+        Err(_) => {
+            tracing::warn!(%remote, "supervisor reply dropped; dropping peer");
+            return;
+        }
+    };
+
+    let (quic_send, quic_recv) = match conn.accept_bi().await {
+        Ok(s) => s,
+        Err(e) => {
+            tracing::warn!(%remote, "accept_bi failed: {e:#}");
+            let _ = sup_tx.send(SupervisorMsg::RemoveViewer { id: id_str }).await;
+            return;
+        }
+    };
+
+    eprintln!("[pixelpass] viewer connected: {remote}");
+
+    let tcp = match serve::connect_to_capture(port, Duration::from_secs(5)).await {
+        Ok(t) => t,
+        Err(e) => {
+            tracing::warn!(%remote, "connect_to_capture failed: {e:#}");
+            let _ = sup_tx.send(SupervisorMsg::RemoveViewer { id: id_str }).await;
+            return;
+        }
+    };
+
+    let bridge = tunnel::bridge(quic_send, quic_recv, tcp);
+    tokio::select! {
+        res = bridge => match res {
+            Ok(()) => tracing::info!(%remote, "bridge closed cleanly"),
+            Err(e) => tracing::info!(%remote, "bridge ended: {e:#}"),
+        },
         _ = cancel.cancelled() => {
-            tracing::info!("cancellation requested during stream");
+            tracing::info!(%remote, "cancellation during stream");
+        }
+        _ = peer_cancel.cancelled() => {
+            tracing::info!(%remote, "kicked by host");
         }
     }
 
-    capture_handle.shutdown().await;
-    Ok(())
+    eprintln!("[pixelpass] viewer disconnected: {remote}");
+    let _ = sup_tx.send(SupervisorMsg::RemoveViewer { id: id_str }).await;
+}
+
+/// Owns the single shared CaptureHandle and the active viewer count. Spawns
+/// capture lazily on the first AddViewer; tears it down when the count drops
+/// back to zero. Enforces the max-viewers cap by refusing AddViewer when
+/// the count is already at the cap.
+async fn supervise(
+    opts: HostOpts,
+    quality: EffectiveQuality,
+    display: DisplayServer,
+    max_viewers: u32,
+    mut rx: mpsc::Receiver<SupervisorMsg>,
+) {
+    let mut handle: Option<CaptureHandle> = None;
+    let mut count: u32 = 0;
+    let mut viewers: HashMap<String, CancellationToken> = HashMap::new();
+
+    while let Some(msg) = rx.recv().await {
+        match msg {
+            SupervisorMsg::AddViewer { id, cancel, reply } => {
+                if count >= max_viewers {
+                    let reason =
+                        format!("host is full ({count} of {max_viewers} viewers connected)");
+                    output::emit(output::Event::ViewerRefused { reason: &reason });
+                    let _ = reply.send(Err(reason));
+                    continue;
+                }
+
+                if handle.is_none() {
+                    tracing::info!("first viewer arriving — spawning capture");
+                    match capture::spawn(display, &opts, &quality).await {
+                        Ok(h) => {
+                            handle = Some(h);
+                            output::emit(output::Event::Capture {
+                                state: output::CaptureState::Started,
+                            });
+                        }
+                        Err(e) => {
+                            let _ = reply.send(Err(format!("capture spawn failed: {e:#}")));
+                            continue;
+                        }
+                    }
+                }
+
+                let port = handle.as_ref().expect("handle was just set").local_port();
+                count += 1;
+                viewers.insert(id.clone(), cancel);
+                let _ = reply.send(Ok(port));
+                output::emit(output::Event::ViewerJoined { id: &id, active: count, max: max_viewers });
+                tracing::info!(active = count, cap = max_viewers, "viewer joined");
+            }
+            SupervisorMsg::RemoveViewer { id } => {
+                viewers.remove(&id);
+                count = count.saturating_sub(1);
+                output::emit(output::Event::ViewerLeft { id: &id, active: count, max: max_viewers });
+                tracing::info!(active = count, cap = max_viewers, "viewer left");
+                if count == 0
+                    && let Some(h) = handle.take()
+                {
+                    tracing::info!("last viewer left — tearing down capture");
+                    h.shutdown().await;
+                    output::emit(output::Event::Capture {
+                        state: output::CaptureState::Stopped,
+                    });
+                }
+            }
+            SupervisorMsg::KickViewer { id } => {
+                if let Some(cancel) = viewers.get(&id) {
+                    tracing::info!(%id, "kicking viewer");
+                    cancel.cancel();
+                }
+            }
+        }
+    }
+
+    if let Some(h) = handle.take() {
+        tracing::info!("host shutdown — tearing down capture");
+        h.shutdown().await;
+        output::emit(output::Event::Capture {
+            state: output::CaptureState::Stopped,
+        });
+    }
 }
 
 fn print_host_banner(
     ticket: &EndpointTicket,
     display: DisplayServer,
     opts: &HostOpts,
+    quality: &EffectiveQuality,
+    resolution: &MaxViewersResolution,
     clipboard_ok: bool,
 ) {
     eprintln!();
     eprintln!("┌─ PixelPass · host ─────────────────────────────────────────");
     eprintln!("│  display server : {display:?}");
     eprintln!("│  capture        : {}", capture_summary(opts));
-    eprintln!("│  bitrate / fps  : {} kbps @ {} fps", opts.bitrate, opts.framerate);
-    eprintln!("│  hw encode      : {}", if opts.no_hwencode { "off" } else { "auto (VAAPI if available)" });
+    eprintln!("│  quality        : {} — {}", quality.label, quality.dimensions_summary());
+    eprintln!("│                   ({})", quality.note);
+    eprintln!("│  hw encode      : {}", if opts.no_hwencode { "off (software x264)" } else { "on (VAAPI H.264)" });
+    eprintln!("│  max viewers    : {} ({})", resolution.value, resolution.source.label());
     eprintln!("│");
     if clipboard_ok {
         eprintln!("│  Your share code has been copied to your clipboard.");
-        eprintln!("│  Send it to your viewer. (If clipboard didn't work, the");
+        eprintln!("│  Send it to your viewer(s). (If clipboard didn't work, the");
         eprintln!("│  code is also shown below for manual copy.)");
     } else {
-        eprintln!("│  Share this ticket with your viewer:");
+        eprintln!("│  Share this ticket with your viewer(s):");
     }
     eprintln!("│");
     eprintln!("│      pixelpass {ticket}");
     eprintln!("│");
-    eprintln!("│  Capture will not start until the viewer connects.");
-    eprintln!("│  Press Ctrl+C to stop.");
+    eprintln!("│  Capture starts when the first viewer connects, runs while");
+    eprintln!("│  any viewer is connected, and tears down when the last one");
+    eprintln!("│  leaves. Press Ctrl+C to stop the host entirely.");
     eprintln!("└────────────────────────────────────────────────────────────");
     eprintln!();
 }
 
+/// How we arrived at the final viewer cap. Surfaced in the banner so the
+/// user can tell at a glance whether the number is what they specified,
+/// what their measured upstream supports, or just the fallback default.
+struct MaxViewersResolution {
+    value: u32,
+    source: MaxViewersSource,
+}
+
+enum MaxViewersSource {
+    /// User passed --max-viewers explicitly.
+    UserFlag,
+    /// Derived from the saved bandwidth measurement.
+    BandwidthMeasurement { safe_mbps: f64 },
+    /// No flag, no measurement — falling back.
+    DefaultFallback,
+}
+
+impl MaxViewersSource {
+    fn label(&self) -> String {
+        match self {
+            MaxViewersSource::UserFlag => "user-specified".to_string(),
+            MaxViewersSource::BandwidthMeasurement { safe_mbps } => {
+                format!("auto: {safe_mbps:.1} Mbps measured upstream")
+            }
+            MaxViewersSource::DefaultFallback => {
+                "default — run `pixelpass --reconfigure` for a connection-aware value".to_string()
+            }
+        }
+    }
+}
+
+fn resolve_max_viewers(opts: &HostOpts, effective_bitrate: u32) -> MaxViewersResolution {
+    if let Some(n) = opts.max_viewers {
+        return MaxViewersResolution {
+            value: n,
+            source: MaxViewersSource::UserFlag,
+        };
+    }
+    if let Ok(cfg) = config::load()
+        && cfg.bandwidth.status == BandwidthStatus::Measured
+        && let Some(upstream) = cfg.bandwidth.upstream_mbps
+    {
+        let n = bandwidth::recommended_max_viewers(upstream, effective_bitrate);
+        return MaxViewersResolution {
+            value: n,
+            source: MaxViewersSource::BandwidthMeasurement { safe_mbps: upstream },
+        };
+    }
+    MaxViewersResolution {
+        value: 2,
+        source: MaxViewersSource::DefaultFallback,
+    }
+}
+
 fn copy_to_clipboard(text: &str) -> bool {
     match arboard::Clipboard::new().and_then(|mut cb| cb.set_text(text.to_owned())) {
         Ok(()) => true,
@@ -140,8 +424,5 @@ fn capture_summary(opts: &HostOpts) -> String {
     } else {
         bits.push("system-audio".to_string());
     }
-    if opts.mic {
-        bits.push("mic".to_string());
-    }
     bits.join(" + ")
 }

src/host/pipeline.rs

@@ -0,0 +1,326 @@
+//! Display-server-agnostic capture pipeline. The video *source* element is the
+//! only part that differs between Wayland (`pipewiresrc`, after a portal
+//! handshake) and X11 (`ximagesrc`); everything downstream — the videorate cap,
+//! the encoder, `h264parse`, `mpegtsmux`, the whole audio branch, the gst spawn,
+//! the [`Serve`] fanout binding, and the [`CaptureHandle`] lifecycle — is shared
+//! and lives here. Backends call [`spawn`] with just their source-element args.
+
+use anyhow::{Context, Result, bail};
+use nix::sys::signal::{Signal, kill};
+use nix::unistd::Pid;
+use std::process::Stdio;
+use std::time::Duration;
+use tokio::process::{Child, Command};
+use tokio::time::timeout;
+
+use super::audio::Routing;
+use super::quality::EffectiveQuality;
+use super::serve::Serve;
+use crate::cli::HostOpts;
+
+pub struct CaptureHandle {
+    gst: Option<Child>,
+    audio: Option<Routing>,
+    serve: Option<Serve>,
+}
+
+impl CaptureHandle {
+    pub fn local_port(&self) -> u16 {
+        self.serve
+            .as_ref()
+            .expect("serve is always Some until shutdown")
+            .local_port()
+    }
+
+    /// Graceful teardown: SIGTERM gst, give it ~1s to exit, then SIGKILL,
+    /// unload audio routing (if any), then tear down the serve layer.
+    /// The serve reader will see EOF on gst stdout and exit on its own;
+    /// serve.shutdown() is the backstop.
+    pub async fn shutdown(mut self) {
+        if let Some(child) = self.gst.as_mut()
+            && let Some(pid) = child.id()
+        {
+            let _ = kill(Pid::from_raw(pid as i32), Signal::SIGTERM);
+        }
+        if let Some(child) = self.gst.as_mut() {
+            let _ = timeout(Duration::from_millis(1000), child.wait()).await;
+            let _ = child.start_kill();
+        }
+        if let Some(audio) = self.audio.take() {
+            audio.shutdown();
+        }
+        if let Some(serve) = self.serve.take() {
+            serve.shutdown().await;
+        }
+    }
+}
+
+impl Drop for CaptureHandle {
+    fn drop(&mut self) {
+        if let Some(child) = self.gst.as_mut() {
+            let _ = child.start_kill();
+        }
+        // Routing's and Serve's own Drop impls handle the rest.
+    }
+}
+
+/// Spawn the shared gst pipeline for a backend that supplies `source_args`
+/// (the video-source element + its properties, e.g. `["pipewiresrc", "fd=7",
+/// …]` or `["ximagesrc", "use-damage=false", …]`). `source_dims` is the source
+/// pixel size when the backend knows it (Wayland from the portal, X11 from
+/// root/window geometry); it lets a downscale preset compute an exact even
+/// target resolution and skip scaling when the source is already small enough.
+/// `after_spawn` runs once, immediately after the gst child is launched —
+/// Wayland uses it to `close` the pipewire fd it leaked into the child; X11
+/// passes a no-op.
+pub async fn spawn(
+    opts: &HostOpts,
+    quality: &EffectiveQuality,
+    source_dims: Option<(u32, u32)>,
+    source_args: Vec<String>,
+    after_spawn: impl FnOnce(),
+) -> Result<CaptureHandle> {
+    let (audio_routing, audio_device) = setup_audio(opts).await?;
+    let args = build_args(&source_args, &audio_device, opts, quality, source_dims);
+
+    let mut gst_cmd = Command::new("gst-launch-1.0");
+    gst_cmd
+        .args(&args)
+        .stdin(Stdio::null())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::inherit());
+    if std::env::var_os("PIXELPASS_GST_DEBUG").is_some() {
+        gst_cmd.env("GST_DEBUG", "3");
+    }
+    let mut gst = gst_cmd.spawn().context("failed to spawn gst-launch-1.0")?;
+
+    // Backend-specific post-spawn cleanup (Wayland closes its leaked pw fd here,
+    // once gst has inherited its own copy).
+    after_spawn();
+
+    let gst_stdout = gst
+        .stdout
+        .take()
+        .context("gst-launch-1.0 stdout pipe unavailable")?;
+
+    // Hand stdout to the serve layer, which binds the localhost HTTP listener
+    // and runs the broadcast fanout. No demux/remux, no codec assumptions.
+    let serve = Serve::bind(gst_stdout).await?;
+
+    Ok(CaptureHandle {
+        gst: Some(gst),
+        audio: audio_routing,
+        serve: Some(serve),
+    })
+}
+
+/// Decide whether per-app audio routing is active and produce the `device=…`
+/// argument for `pulsesrc`. Routing activates when either `--app` is set
+/// (per-stream rerouting to a per-PID null-sink) or `PIXELPASS_AUDIO_VIA_NULL_SINK=1`
+/// is set (no app filter — captures everything via the null-sink, used for
+/// dogfooding the loopback path). Otherwise we capture the default sink's
+/// monitor (system audio out), not the default source (the mic).
+async fn setup_audio(opts: &HostOpts) -> Result<(Option<Routing>, String)> {
+    let routing_requested =
+        opts.app.is_some() || std::env::var_os("PIXELPASS_AUDIO_VIA_NULL_SINK").is_some();
+    let audio_routing = if routing_requested {
+        Some(
+            Routing::start(opts)
+                .await
+                .context("audio routing setup failed")?,
+        )
+    } else {
+        None
+    };
+    let audio_device = if let Some(r) = &audio_routing {
+        format!("device={}.monitor", r.sink_name())
+    } else {
+        let default = default_audio_monitor().await?;
+        format!("device={default}")
+    };
+    Ok((audio_routing, audio_device))
+}
+
+/// Build the full gst-launch argument vector: MPEG-TS mux + fdsink, then the
+/// video branch (caller's `source` → videorate cap → optional downscale →
+/// encoder → h264parse → mux.), then the audio branch (pulsesrc → AAC → mux.).
+/// Bitrate, framerate, and the downscale height come from the resolved
+/// [`EffectiveQuality`]; the encoder and the `videoconvert` target format are
+/// selected by `opts.no_hwencode` (hardware VAAPI wants NV12, software x264
+/// wants I420).
+fn build_args(
+    source: &[String],
+    audio_device: &str,
+    opts: &HostOpts,
+    quality: &EffectiveQuality,
+    source_dims: Option<(u32, u32)>,
+) -> Vec<String> {
+    let key_interval = (quality.framerate * 2).to_string();
+    let bitrate = quality.bitrate.to_string();
+    let framerate_caps = format!("video/x-raw,framerate={}/1", quality.framerate);
+
+    let (raw_format, encoder_args): (&str, Vec<String>) = if opts.no_hwencode {
+        (
+            "video/x-raw,format=I420",
+            vec![
+                "x264enc".into(),
+                "tune=zerolatency".into(),
+                "speed-preset=ultrafast".into(),
+                format!("bitrate={bitrate}"),
+                format!("key-int-max={key_interval}"),
+            ],
+        )
+    } else {
+        (
+            "video/x-raw,format=NV12",
+            vec![
+                "vah264enc".into(),
+                "rate-control=cbr".into(),
+                format!("bitrate={bitrate}"),
+                format!("key-int-max={key_interval}"),
+            ],
+        )
+    };
+
+    // muxer + sink
+    let mut args: Vec<String> = vec![
+        "mpegtsmux".into(),
+        "name=mux".into(),
+        "!".into(),
+        "queue".into(),
+        "!".into(),
+        "fdsink".into(),
+        "fd=1".into(),
+    ];
+
+    // Downscale step for the quality presets. `None` = encode at native size
+    // (the "Source" preset, or a source already at/below the target height — we
+    // never upscale). When the source dimensions are known we pin an exact even
+    // WxH preserving the source aspect; H.264 4:2:0 needs even dims, so width is
+    // rounded to even and height is forced even (preset heights already are; a
+    // raw --max-height override is rounded down). When dims are unknown (a rare
+    // X11 geometry-read failure) we fall back to height-only + square pixels +
+    // an even-stepped width range and let videoscale negotiate.
+    let scale_caps: Option<String> = match quality.max_height {
+        None => {
+            tracing::info!(preset = %quality.label, "encoding at native resolution (no downscale)");
+            None
+        }
+        Some(max_h) => {
+            let h = (max_h & !1).max(2);
+            match source_dims {
+                Some((sw, sh)) if sh > h => {
+                    let w = ((sw as u64 * h as u64 + sh as u64 / 2) / sh as u64) as u32;
+                    let w = (w & !1).max(2);
+                    tracing::info!(
+                        preset = %quality.label,
+                        from = %format!("{sw}x{sh}"),
+                        to = %format!("{w}x{h}"),
+                        "downscaling video"
+                    );
+                    Some(format!("{raw_format},width={w},height={h}"))
+                }
+                Some((sw, sh)) => {
+                    tracing::info!(
+                        preset = %quality.label,
+                        source = %format!("{sw}x{sh}"),
+                        max_height = h,
+                        "source already at/below preset height — encoding native (no upscale)"
+                    );
+                    None
+                }
+                None => {
+                    tracing::info!(
+                        preset = %quality.label,
+                        max_height = h,
+                        "downscaling to max height (source size unknown — width follows negotiation)"
+                    );
+                    Some(format!(
+                        "{raw_format},height={h},pixel-aspect-ratio=1/1,width=[2,8192,2]"
+                    ))
+                }
+            }
+        }
+    };
+
+    // video branch — videorate caps to the target fps so we don't ship at the
+    // monitor's refresh rate (e.g. 180Hz) and pile up frames in the demuxer
+    // queue faster than realtime. videoscale (when scaling) runs *after*
+    // videoconvert so it operates on system-memory NV12/I420: scaling
+    // pipewiresrc's raw output directly can hit a format/memory (e.g. DMABuf)
+    // that software videoscale won't negotiate.
+    args.extend(source.iter().cloned());
+    args.extend([
+        "!".into(),
+        "videorate".into(),
+        "!".into(),
+        framerate_caps,
+        "!".into(),
+        "queue".into(),
+        "!".into(),
+        "videoconvert".into(),
+        "!".into(),
+        raw_format.into(),
+        "!".into(),
+    ]);
+    if let Some(caps) = scale_caps {
+        args.extend(["videoscale".into(), "!".into(), caps, "!".into()]);
+    }
+    args.extend(encoder_args);
+    args.extend([
+        "!".into(),
+        "h264parse".into(),
+        "config-interval=-1".into(),
+        "!".into(),
+        "video/x-h264,stream-format=byte-stream,alignment=au".into(),
+        "!".into(),
+        "mux.".into(),
+    ]);
+
+    // audio branch — capture the default sink's MONITOR (system audio out),
+    // not the default source (which is the mic).
+    args.extend([
+        "pulsesrc".into(),
+        audio_device.to_string(),
+        "do-timestamp=true".into(),
+        "!".into(),
+        "queue".into(),
+        "!".into(),
+        "audioconvert".into(),
+        "!".into(),
+        "audioresample".into(),
+        "!".into(),
+        "audio/x-raw,rate=48000,channels=2".into(),
+        "!".into(),
+        "avenc_aac".into(),
+        "bitrate=128000".into(),
+        "!".into(),
+        "aacparse".into(),
+        "!".into(),
+        "mux.".into(),
+    ]);
+
+    args
+}
+
+async fn default_audio_monitor() -> Result<String> {
+    let output = Command::new("pactl")
+        .arg("get-default-sink")
+        .output()
+        .await
+        .context("failed to run `pactl get-default-sink` (install pulseaudio-utils or pipewire-pulse)")?;
+    if !output.status.success() {
+        bail!(
+            "pactl get-default-sink failed: {}",
+            String::from_utf8_lossy(&output.stderr).trim()
+        );
+    }
+    let sink = String::from_utf8(output.stdout)
+        .context("default sink name was not UTF-8")?
+        .trim()
+        .to_string();
+    if sink.is_empty() {
+        bail!("pactl get-default-sink returned no name (is a sound server running?)");
+    }
+    Ok(format!("{sink}.monitor"))
+}

src/host/quality.rs

@@ -0,0 +1,257 @@
+//! Resolution / quality presets. A preset bundles `(max_height, bitrate, fps)`
+//! because resolution is a *quality-per-bitrate* knob, not a standalone one —
+//! the three are only useful together. Quality is **host-global**: one encode
+//! pipeline fans out to every viewer over the broadcast channel, so the sharer
+//! picks one quality for everyone (per-viewer quality would need per-viewer
+//! encodes, which kills the fanout).
+//!
+//! [`resolve`] turns the raw CLI/picker choice into a concrete
+//! [`EffectiveQuality`] the pipeline encodes at, applying — in order — the
+//! chosen preset (or an Auto derivation from the bandwidth pre-flight), then
+//! any explicit `--bitrate` / `--framerate` / `--max-height` field overrides.
+
+use crate::cli::{HostOpts, Quality};
+use crate::common::{config, config::BandwidthStatus};
+
+/// A fixed preset's concrete settings. `max_height = None` means encode at the
+/// native source resolution (no `videoscale` element is inserted at all).
+#[derive(Debug, Clone, Copy)]
+struct Preset {
+    max_height: Option<u32>,
+    bitrate: u32, // kbps
+    framerate: u32,
+}
+
+impl Quality {
+    /// The fixed tuple for a preset. `Auto` returns `None` — it has no fixed
+    /// values and resolves to one of the others at runtime (see [`resolve_auto`]).
+    fn preset(self) -> Option<Preset> {
+        let p = match self {
+            Quality::Source => Preset { max_height: None, bitrate: 6000, framerate: 30 },
+            Quality::High => Preset { max_height: Some(1080), bitrate: 4000, framerate: 30 },
+            Quality::Medium => Preset { max_height: Some(720), bitrate: 2500, framerate: 30 },
+            Quality::Low => Preset { max_height: Some(480), bitrate: 1000, framerate: 30 },
+            Quality::Auto => return None,
+        };
+        Some(p)
+    }
+
+    fn name(self) -> &'static str {
+        match self {
+            Quality::Source => "Source",
+            Quality::High => "High",
+            Quality::Medium => "Medium",
+            Quality::Low => "Low",
+            Quality::Auto => "Auto",
+        }
+    }
+}
+
+/// Fixed presets in descending quality order — Auto walks this to find the
+/// best one whose per-viewer bitrate fits the measured upstream budget.
+const AUTO_LADDER: [Quality; 4] = [Quality::Source, Quality::High, Quality::Medium, Quality::Low];
+
+/// Auto's fallback when there is no usable bandwidth measurement.
+const AUTO_FALLBACK: Quality = Quality::Medium;
+
+/// Fully-resolved quality: the concrete values the pipeline will encode at,
+/// plus human-readable strings for the host banner.
+#[derive(Debug, Clone)]
+pub struct EffectiveQuality {
+    /// `None` = native resolution (omit `videoscale`); `Some(h)` = scale to height `h`.
+    pub max_height: Option<u32>,
+    pub bitrate: u32, // kbps
+    pub framerate: u32,
+    /// Short label, e.g. `"High"` or `"Auto → Medium"`.
+    pub label: String,
+    /// Provenance note for the banner, e.g. `"user-specified"` or
+    /// `"auto: 8.8 Mbps safe ÷ 1 viewer"`.
+    pub note: String,
+}
+
+impl EffectiveQuality {
+    /// `WxH-ish / bitrate / fps` summary for the banner. Width is unknown until
+    /// capture (the source dictates it), so height is shown as `?xN` / `native`.
+    pub fn dimensions_summary(&self) -> String {
+        let res = match self.max_height {
+            Some(h) => format!("≤{h}p"),
+            None => "native".to_string(),
+        };
+        format!("{res} / {} kbps / {} fps", self.bitrate, self.framerate)
+    }
+}
+
+/// Resolve the host's quality choice into concrete encode settings.
+///
+/// `sizing_viewers` is the viewer count Auto sizes its budget against (the
+/// resolved `--max-viewers` cap, so quality is chosen for the worst case —
+/// quality is baked in at capture-spawn and can't drop when viewer #2 joins).
+pub fn resolve(opts: &HostOpts, sizing_viewers: u32) -> EffectiveQuality {
+    // 1. Base preset: a fixed tuple, or an Auto derivation.
+    let (base, label, base_note) = match opts.quality {
+        Quality::Auto => resolve_auto(measured_safe_mbps(), sizing_viewers),
+        q => {
+            let p = q.preset().expect("non-Auto presets always have a tuple");
+            (p, q.name().to_string(), "user-specified".to_string())
+        }
+    };
+
+    let mut eff = EffectiveQuality {
+        max_height: base.max_height,
+        bitrate: base.bitrate,
+        framerate: base.framerate,
+        label,
+        note: base_note,
+    };
+
+    // 2. Per-field overrides win over the preset (precedence rule).
+    let mut overridden = Vec::new();
+    if let Some(b) = opts.bitrate {
+        eff.bitrate = b;
+        overridden.push("bitrate");
+    }
+    if let Some(f) = opts.framerate {
+        eff.framerate = f;
+        overridden.push("fps");
+    }
+    if let Some(h) = opts.max_height {
+        eff.max_height = Some(h);
+        overridden.push("max-height");
+    }
+    if !overridden.is_empty() {
+        eff.note = format!("{}; override: {}", eff.note, overridden.join(", "));
+    }
+
+    eff
+}
+
+/// Auto: pick the highest preset whose per-viewer bitrate fits the measured
+/// safe upstream divided by the viewer count. Falls back to [`AUTO_FALLBACK`]
+/// when there's no usable measurement. Pure (no config I/O) so it's testable;
+/// [`resolve`] supplies the measurement via [`measured_safe_mbps`].
+fn resolve_auto(safe_mbps: Option<f64>, sizing_viewers: u32) -> (Preset, String, String) {
+    match safe_mbps {
+        Some(safe_mbps) => {
+            let n = sizing_viewers.max(1);
+            let budget_mbps = safe_mbps / n as f64;
+            let chosen = AUTO_LADDER
+                .iter()
+                .copied()
+                .find(|q| {
+                    let kbps = q.preset().expect("ladder is fixed presets").bitrate;
+                    (kbps as f64) / 1000.0 <= budget_mbps
+                })
+                .unwrap_or(Quality::Low);
+            let preset = chosen.preset().expect("ladder is fixed presets");
+            (
+                preset,
+                format!("Auto → {}", chosen.name()),
+                format!("auto: {safe_mbps:.1} Mbps safe ÷ {n} viewer(s) = {budget_mbps:.1} Mbps each"),
+            )
+        }
+        None => {
+            let preset = AUTO_FALLBACK.preset().expect("fallback is a fixed preset");
+            (
+                preset,
+                format!("Auto → {}", AUTO_FALLBACK.name()),
+                "auto fallback — no bandwidth measurement (run `pixelpass --reconfigure`)".to_string(),
+            )
+        }
+    }
+}
+
+/// The saved safe-upstream figure, only when the pre-flight actually measured
+/// one. Skipped/failed/unmeasured all return `None` so Auto falls back.
+fn measured_safe_mbps() -> Option<f64> {
+    let cfg = config::load().ok()?;
+    if cfg.bandwidth.status == BandwidthStatus::Measured {
+        cfg.bandwidth.upstream_mbps
+    } else {
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::cli::{DisplayServerArg, HostOpts};
+
+    /// A HostOpts with no overrides, parameterized by quality + max_viewers.
+    fn opts(quality: Quality, max_viewers: Option<u32>) -> HostOpts {
+        HostOpts {
+            window: false,
+            app: None,
+            display_server: None::<DisplayServerArg>,
+            quality,
+            bitrate: None,
+            framerate: None,
+            max_height: None,
+            no_hwencode: false,
+            max_viewers,
+            interactive: false,
+        }
+    }
+
+    #[test]
+    fn fixed_presets_pass_through_their_tuple() {
+        let e = resolve(&opts(Quality::Medium, None), 1);
+        assert_eq!(e.max_height, Some(720));
+        assert_eq!(e.bitrate, 2500);
+        assert_eq!(e.framerate, 30);
+        assert_eq!(e.label, "Medium");
+        assert_eq!(e.note, "user-specified");
+
+        // Source is the native (no-scale) preset.
+        assert_eq!(resolve(&opts(Quality::Source, None), 1).max_height, None);
+    }
+
+    #[test]
+    fn auto_picks_highest_preset_that_fits_budget() {
+        // Ample upstream, single viewer → Source fits (6 Mbps <= 8.78).
+        let (p, label, _) = resolve_auto(Some(8.78), 1);
+        assert_eq!(p.bitrate, 6000);
+        assert_eq!(label, "Auto → Source");
+
+        // 10 Mbps split across 2 viewers = 5 each → Source(6) no, High(4) yes.
+        let (p, label, _) = resolve_auto(Some(10.0), 2);
+        assert_eq!(p.bitrate, 4000);
+        assert_eq!(label, "Auto → High");
+
+        // Tight budget falls to the bottom of the ladder, never below Low.
+        let (p, _, _) = resolve_auto(Some(0.3), 1);
+        assert_eq!(p.bitrate, 1000); // Low
+    }
+
+    #[test]
+    fn auto_without_measurement_falls_back_to_medium() {
+        let (p, label, note) = resolve_auto(None, 1);
+        assert_eq!(p.bitrate, 2500); // Medium
+        assert_eq!(p.max_height, Some(720));
+        assert_eq!(label, "Auto → Medium");
+        assert!(note.contains("reconfigure"));
+    }
+
+    #[test]
+    fn explicit_flags_override_preset_fields() {
+        let mut o = opts(Quality::High, None);
+        o.bitrate = Some(9000);
+        o.framerate = Some(60);
+        let e = resolve(&o, 1);
+        assert_eq!(e.bitrate, 9000); // override wins
+        assert_eq!(e.framerate, 60); // override wins
+        assert_eq!(e.max_height, Some(1080)); // untouched preset field
+        assert!(e.note.contains("override: bitrate, fps"));
+    }
+
+    #[test]
+    fn max_height_override_is_rounded_even_and_applies_to_source() {
+        // Odd override rounds down to even in the pipeline; here we just assert
+        // the override replaces the (native) Source height with the raw value;
+        // the even-rounding happens in pipeline::build_args.
+        let mut o = opts(Quality::Source, None);
+        o.max_height = Some(900);
+        let e = resolve(&o, 1);
+        assert_eq!(e.max_height, Some(900));
+        assert!(e.note.contains("override: max-height"));
+    }
+}

src/host/serve.rs

@@ -0,0 +1,191 @@
+//! Display-server-agnostic serving layer: takes a capture child's stdout
+//! producing MPEG-TS bytes and fans them out to N concurrent HTTP viewers
+//! on a localhost port. One reader task pumps stdout chunks into a
+//! tokio::sync::broadcast channel; the accept loop spawns one drain task
+//! per accepted TCP connection. Slow consumers see Lagged and skip ahead;
+//! MPEG-TS resyncs at the next keyframe.
+//!
+//! Backends (host/wayland.rs, future host/x11.rs) build their own gst
+//! pipeline and hand the resulting ChildStdout to [`Serve::bind`].
+
+use anyhow::{Context, Result, bail};
+use std::sync::Arc;
+use std::time::Duration;
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::{TcpListener, TcpStream};
+use tokio::process::ChildStdout;
+use tokio::sync::broadcast;
+use tokio::task::JoinHandle;
+use tokio::time::{Instant, sleep};
+
+/// Broadcast-channel capacity in chunks. Each chunk is up to 64 KiB from
+/// the capture child's stdout, so 16 chunks ≈ 1 MiB ≈ ~2 s of buffered
+/// jitter at typical bitrates. A viewer that falls behind by more than
+/// this gets Lagged and skips ahead — MPEG-TS recovers at the next
+/// keyframe.
+const FANOUT_CAPACITY: usize = 16;
+
+/// Size of each chunk read from the capture child's stdout.
+const READ_CHUNK: usize = 64 * 1024;
+
+/// Owns the localhost HTTP listener and the two long-running tasks that
+/// pump bytes from a capture child to all connected viewers.
+pub struct Serve {
+    port: u16,
+    reader: Option<JoinHandle<()>>,
+    server: Option<JoinHandle<()>>,
+}
+
+impl Serve {
+    /// Bind a localhost listener on a random port, set up the broadcast
+    /// fanout, and spawn the reader + accept-loop tasks. The provided
+    /// `stdout` is assumed to produce MPEG-TS bytes.
+    pub async fn bind(stdout: ChildStdout) -> Result<Self> {
+        let listener = TcpListener::bind("127.0.0.1:0")
+            .await
+            .context("could not bind local capture HTTP listener")?;
+        let port = listener.local_addr()?.port();
+
+        let (tx, _) = broadcast::channel::<Arc<Vec<u8>>>(FANOUT_CAPACITY);
+        let reader = tokio::spawn(pump_to_broadcast(stdout, tx.clone()));
+        let server = tokio::spawn(run_accept_loop(listener, tx));
+
+        Ok(Self {
+            port,
+            reader: Some(reader),
+            server: Some(server),
+        })
+    }
+
+    pub fn local_port(&self) -> u16 {
+        self.port
+    }
+
+    /// Abort the reader and accept-loop tasks. Backends typically call this
+    /// after killing their capture child so the reader sees stdout EOF and
+    /// exits on its own; the abort is a backstop.
+    pub async fn shutdown(mut self) {
+        if let Some(task) = self.reader.take() {
+            task.abort();
+        }
+        if let Some(task) = self.server.take() {
+            task.abort();
+        }
+    }
+}
+
+impl Drop for Serve {
+    fn drop(&mut self) {
+        if let Some(task) = self.reader.as_ref() {
+            task.abort();
+        }
+        if let Some(task) = self.server.as_ref() {
+            task.abort();
+        }
+    }
+}
+
+/// Connect to the local capture HTTP listener, retrying until it's up or
+/// we time out. Returns the connected socket — the bridge layer pipes
+/// QUIC↔this socket once it's open.
+pub async fn connect_to_capture(port: u16, max_wait: Duration) -> Result<TcpStream> {
+    let deadline = Instant::now() + max_wait;
+    loop {
+        match TcpStream::connect(("127.0.0.1", port)).await {
+            Ok(stream) => return Ok(stream),
+            Err(_) if Instant::now() < deadline => {
+                sleep(Duration::from_millis(50)).await;
+            }
+            Err(e) => bail!("capture HTTP listener never came up on 127.0.0.1:{port}: {e}"),
+        }
+    }
+}
+
+/// Read the capture child's stdout in chunks and broadcast each to all
+/// current subscribers. `broadcast::send` returns Err when there are no
+/// receivers; we ignore it so the capture child isn't backpressured
+/// waiting for a viewer.
+async fn pump_to_broadcast(mut stdout: ChildStdout, tx: broadcast::Sender<Arc<Vec<u8>>>) {
+    let mut buf = vec![0u8; READ_CHUNK];
+    loop {
+        match stdout.read(&mut buf).await {
+            Ok(0) => {
+                tracing::info!("capture stdout EOF — fanout reader exiting");
+                return;
+            }
+            Ok(n) => {
+                let chunk = Arc::new(buf[..n].to_vec());
+                let _ = tx.send(chunk);
+            }
+            Err(e) => {
+                tracing::warn!("capture stdout read error: {e}");
+                return;
+            }
+        }
+    }
+}
+
+async fn run_accept_loop(listener: TcpListener, tx: broadcast::Sender<Arc<Vec<u8>>>) {
+    loop {
+        let sock = match listener.accept().await {
+            Ok((s, _)) => s,
+            Err(e) => {
+                tracing::warn!("capture HTTP accept failed: {e}");
+                return;
+            }
+        };
+        let rx = tx.subscribe();
+        tokio::spawn(serve_one_viewer(sock, rx));
+    }
+}
+
+async fn serve_one_viewer(mut sock: TcpStream, mut rx: broadcast::Receiver<Arc<Vec<u8>>>) {
+    if !drain_http_request(&mut sock).await {
+        return;
+    }
+
+    const RESPONSE: &[u8] = b"HTTP/1.1 200 OK\r\n\
+        Content-Type: video/mp2t\r\n\
+        Cache-Control: no-cache, no-store\r\n\
+        Connection: close\r\n\
+        \r\n";
+    if sock.write_all(RESPONSE).await.is_err() {
+        return;
+    }
+
+    loop {
+        match rx.recv().await {
+            Ok(chunk) => {
+                if sock.write_all(&chunk).await.is_err() {
+                    return;
+                }
+            }
+            Err(broadcast::error::RecvError::Lagged(skipped)) => {
+                tracing::warn!(
+                    skipped,
+                    "viewer fanout lagged — MPEG-TS will resync at next keyframe"
+                );
+                continue;
+            }
+            Err(broadcast::error::RecvError::Closed) => return,
+        }
+    }
+}
+
+async fn drain_http_request(sock: &mut TcpStream) -> bool {
+    let mut buf = [0u8; 1024];
+    let mut total = Vec::with_capacity(512);
+    loop {
+        match sock.read(&mut buf).await {
+            Ok(0) => return false,
+            Ok(n) => total.extend_from_slice(&buf[..n]),
+            Err(_) => return false,
+        }
+        if total.windows(4).any(|w| w == b"\r\n\r\n") {
+            return true;
+        }
+        if total.len() > 16 * 1024 {
+            return false;
+        }
+    }
+}

src/host/wayland.rs

@@ -1,9 +1,9 @@
-//! Wayland capture: ashpd ScreenCast portal → PipeWire fd → gst-launch
-//! pipewiresrc → MPEG-TS on gst stdout → in-process HTTP server bound on a
-//! random localhost port. The host bridge TCP-connects to that server and
-//! pumps bytes to QUIC.
+//! Wayland capture: ashpd ScreenCast portal → PipeWire fd → `pipewiresrc`.
+//! This module owns only the portal handshake and the source-element args;
+//! the shared encode/mux tail, gst spawn, and serving live in
+//! [`super::pipeline`].
 
-use anyhow::{Context, Result, bail};
+use anyhow::{Context, Result};
 use ashpd::{
     WindowIdentifier,
     desktop::{
@@ -12,61 +12,14 @@ use ashpd::{
     },
 };
 use nix::fcntl::{FcntlArg, FdFlag, fcntl};
-use nix::sys::signal::{Signal, kill};
-use nix::unistd::{Pid, close};
+use nix::unistd::close;
 use std::os::fd::{AsFd, IntoRawFd, OwnedFd, RawFd};
-use std::process::Stdio;
-use std::time::Duration;
-use tokio::io::{AsyncReadExt, AsyncWriteExt};
-use tokio::net::{TcpListener, TcpStream};
-use tokio::process::{Child, ChildStdout, Command};
-use tokio::task::JoinHandle;
-use tokio::time::{Instant, sleep, timeout};
 
+use super::pipeline::{self, CaptureHandle};
+use super::quality::EffectiveQuality;
 use crate::cli::HostOpts;
 
-pub struct CaptureHandle {
-    port: u16,
-    gst: Option<Child>,
-    server: Option<JoinHandle<()>>,
-}
-
-impl CaptureHandle {
-    pub fn local_port(&self) -> u16 {
-        self.port
-    }
-
-    /// Graceful teardown: SIGTERM gst, give it ~1s to exit, then SIGKILL, then
-    /// abort the HTTP server task. Call this before dropping; Drop only fires
-    /// the kill backstop.
-    pub async fn shutdown(mut self) {
-        if let Some(child) = self.gst.as_mut()
-            && let Some(pid) = child.id()
-        {
-            let _ = kill(Pid::from_raw(pid as i32), Signal::SIGTERM);
-        }
-        if let Some(child) = self.gst.as_mut() {
-            let _ = timeout(Duration::from_millis(1000), child.wait()).await;
-            let _ = child.start_kill();
-        }
-        if let Some(task) = self.server.take() {
-            task.abort();
-        }
-    }
-}
-
-impl Drop for CaptureHandle {
-    fn drop(&mut self) {
-        if let Some(child) = self.gst.as_mut() {
-            let _ = child.start_kill();
-        }
-        if let Some(task) = self.server.as_ref() {
-            task.abort();
-        }
-    }
-}
-
-pub async fn start(opts: &HostOpts) -> Result<CaptureHandle> {
+pub async fn start(opts: &HostOpts, quality: &EffectiveQuality) -> Result<CaptureHandle> {
     // 1. Negotiate the screencast session with the portal.
     let proxy = Screencast::new()
         .await
@@ -105,154 +58,23 @@ pub async fn start(opts: &HostOpts) -> Result<CaptureHandle> {
     tracing::info!(node_id, width = w, height = h, "portal handshake complete");
     // The fd is CLOEXEC by default; the gst child needs to inherit it across
     // exec. We then leak it via into_raw_fd so its lifetime spans the spawn,
-    // and close the parent's copy once gst is running.
+    // and close the parent's copy once gst is running (the pipeline's
+    // after_spawn hook below).
     clear_cloexec(&pw_fd)?;
     let raw_fd: RawFd = pw_fd.into_raw_fd();
 
-    // 2. Bind the in-process HTTP listener on a random localhost port.
-    let listener = TcpListener::bind("127.0.0.1:0")
-        .await
-        .context("could not bind local capture HTTP listener")?;
-    let port = listener.local_addr()?.port();
+    let source_args = vec![
+        "pipewiresrc".to_string(),
+        format!("fd={raw_fd}"),
+        format!("path={node_id}"),
+        "do-timestamp=true".to_string(),
+    ];
 
-    // 3. Spawn gst-launch with the full pipeline: video AND audio captured,
-    //    encoded, and muxed into MPEG-TS inside gst. Output goes to stdout,
-    //    which we pipe straight to our HTTP server task — no demux/remux,
-    //    no codec assumptions.
-    let key_interval = (opts.framerate * 2).to_string();
-    let bitrate = opts.bitrate.to_string();
-    let audio_monitor = default_audio_monitor().await?;
-    let audio_device = format!("device={audio_monitor}");
-    let mut gst_cmd = Command::new("gst-launch-1.0");
-    gst_cmd
-        .args([
-            // muxer + sink
-            "mpegtsmux",
-            "name=mux",
-            "!",
-            "queue",
-            "!",
-            "fdsink",
-            "fd=1",
-            // video branch — videorate caps to 30fps so we don't ship at the
-            // monitor's refresh rate (e.g. 180Hz) and pile up frames in mpv's
-            // demuxer queue faster than realtime.
-            "pipewiresrc",
-            &format!("fd={raw_fd}"),
-            &format!("path={node_id}"),
-            "do-timestamp=true",
-            "!",
-            "videorate",
-            "!",
-            &format!("video/x-raw,framerate={}/1", opts.framerate),
-            "!",
-            "queue",
-            "!",
-            "videoconvert",
-            "!",
-            "video/x-raw,format=NV12",
-            "!",
-            "vah264enc",
-            "rate-control=cbr",
-            &format!("bitrate={bitrate}"),
-            &format!("key-int-max={key_interval}"),
-            "!",
-            "h264parse",
-            "config-interval=-1",
-            "!",
-            "video/x-h264,stream-format=byte-stream,alignment=au",
-            "!",
-            "mux.",
-            // audio branch — capture the default sink's MONITOR (system audio
-            // out), not the default source (which is the mic).
-            "pulsesrc",
-            &audio_device,
-            "do-timestamp=true",
-            "!",
-            "queue",
-            "!",
-            "audioconvert",
-            "!",
-            "audioresample",
-            "!",
-            "audio/x-raw,rate=48000,channels=2",
-            "!",
-            "avenc_aac",
-            "bitrate=128000",
-            "!",
-            "aacparse",
-            "!",
-            "mux.",
-        ])
-        .stdin(Stdio::null())
-        .stdout(Stdio::piped())
-        .stderr(Stdio::inherit());
-    if std::env::var_os("PIXELPASS_GST_DEBUG").is_some() {
-        gst_cmd.env("GST_DEBUG", "3");
-    }
-    let mut gst = gst_cmd.spawn().context("failed to spawn gst-launch-1.0")?;
-    // Parent no longer needs the pipewire fd — gst inherited its own copy.
-    let _ = close(raw_fd);
-
-    let gst_stdout = gst
-        .stdout
-        .take()
-        .context("gst-launch-1.0 stdout pipe unavailable")?;
-
-    // 4. Spawn the HTTP server task. It owns the listener + gst stdout: it
-    //    accepts one client (the host's bridge socket via connect_to_capture),
-    //    drains the HTTP request, writes a fixed MPEG-TS response, then
-    //    copies gst stdout to the socket forever.
-    let server = tokio::spawn(serve_capture(listener, gst_stdout));
-
-    Ok(CaptureHandle {
-        port,
-        gst: Some(gst),
-        server: Some(server),
+    pipeline::spawn(opts, quality, Some((w as u32, h as u32)), source_args, move || {
+        // Parent no longer needs the pipewire fd — gst inherited its own copy.
+        let _ = close(raw_fd);
     })
-}
-
-async fn serve_capture(listener: TcpListener, mut gst_stdout: ChildStdout) {
-    let mut sock = match listener.accept().await {
-        Ok((s, _)) => s,
-        Err(e) => {
-            tracing::warn!("capture HTTP accept failed: {e}");
-            return;
-        }
-    };
-
-    if !drain_http_request(&mut sock).await {
-        return;
-    }
-
-    const RESPONSE: &[u8] = b"HTTP/1.1 200 OK\r\n\
-        Content-Type: video/mp2t\r\n\
-        Cache-Control: no-cache, no-store\r\n\
-        Connection: close\r\n\
-        \r\n";
-    if sock.write_all(RESPONSE).await.is_err() {
-        return;
-    }
-
-    let _ = tokio::io::copy(&mut gst_stdout, &mut sock).await;
-}
-
-async fn drain_http_request(sock: &mut TcpStream) -> bool {
-    let mut buf = [0u8; 1024];
-    let mut total = Vec::with_capacity(512);
-    loop {
-        match sock.read(&mut buf).await {
-            Ok(0) => return false,
-            Ok(n) => total.extend_from_slice(&buf[..n]),
-            Err(_) => return false,
-        }
-        if total.windows(4).any(|w| w == b"\r\n\r\n") {
-            return true;
-        }
-        if total.len() > 16 * 1024 {
-            return false;
-        }
-    }
+    .await
 }
 
 fn clear_cloexec(fd: &impl AsFd) -> Result<()> {
@@ -262,41 +84,3 @@ fn clear_cloexec(fd: &impl AsFd) -> Result<()> {
     fcntl(fd.as_fd(), FcntlArg::F_SETFD(flags)).context("F_SETFD on pipewire fd")?;
     Ok(())
 }
-
-/// Connect to the in-process capture HTTP listener, retrying until it's up or
-/// we time out. Returns the connected socket — the listener accepts exactly
-/// one connection (the bridge socket), so this stream IS the bridge socket.
-pub async fn connect_to_capture(port: u16, max_wait: Duration) -> Result<TcpStream> {
-    let deadline = Instant::now() + max_wait;
-    loop {
-        match TcpStream::connect(("127.0.0.1", port)).await {
-            Ok(stream) => return Ok(stream),
-            Err(_) if Instant::now() < deadline => {
-                sleep(Duration::from_millis(50)).await;
-            }
-            Err(e) => bail!("capture HTTP listener never came up on 127.0.0.1:{port}: {e}"),
-        }
-    }
-}
-
-async fn default_audio_monitor() -> Result<String> {
-    let output = Command::new("pactl")
-        .arg("get-default-sink")
-        .output()
-        .await
-        .context("failed to run `pactl get-default-sink` (install pulseaudio-utils or pipewire-pulse)")?;
-    if !output.status.success() {
-        bail!(
-            "pactl get-default-sink failed: {}",
-            String::from_utf8_lossy(&output.stderr).trim()
-        );
-    }
-    let sink = String::from_utf8(output.stdout)
-        .context("default sink name was not UTF-8")?
-        .trim()
-        .to_string();
-    if sink.is_empty() {
-        bail!("pactl get-default-sink returned no name (is a sound server running?)");
-    }
-    Ok(format!("{sink}.monitor"))
-}

src/host/x11.rs

@@ -0,0 +1,103 @@
+//! X11 capture: `ximagesrc` → the shared encode/mux tail in [`super::pipeline`].
+//! Unlike Wayland there's no portal and no fd hand-off — `ximagesrc` opens its
+//! own X connection from `$DISPLAY`. The whole root window is captured by
+//! default; `--window` resolves a single window's XID via an `xwininfo`
+//! click-picker. The ticket is the access control, so capture starts silently
+//! when the first viewer connects (no host-side consent prompt).
+
+use anyhow::{Context, Result, bail};
+use tokio::process::Command;
+use x11rb::connection::Connection;
+use x11rb::protocol::xproto::ConnectionExt;
+
+use super::pipeline::{self, CaptureHandle};
+use super::quality::EffectiveQuality;
+use crate::cli::HostOpts;
+
+pub async fn start(opts: &HostOpts, quality: &EffectiveQuality) -> Result<CaptureHandle> {
+    let xid = if opts.window {
+        Some(pick_window().await?)
+    } else {
+        None
+    };
+
+    // Geometry mirrors Wayland's portal-handshake log line and feeds the
+    // downscale presets (so they can compute an exact target size). A failure
+    // here shouldn't abort capture — ximagesrc will surface a real error if the
+    // X connection is genuinely unusable, and the scaler falls back to a
+    // height-only negotiation when dims are unknown.
+    let source_dims = match read_geometry(xid) {
+        Ok((w, h)) => {
+            tracing::info!(width = w, height = h, xid = ?xid, "X11 capture geometry");
+            Some((w as u32, h as u32))
+        }
+        Err(e) => {
+            tracing::warn!("could not read X11 geometry (capture will still try): {e:#}");
+            None
+        }
+    };
+
+    let mut source_args = vec![
+        "ximagesrc".to_string(),
+        // Full frames (no damage regions) to avoid partial-update artifacts;
+        // use-damage=true is a later CPU optimization. show-pointer matches
+        // Wayland's CursorMode::Embedded.
+        "use-damage=false".to_string(),
+        "show-pointer=true".to_string(),
+    ];
+    if let Some(xid) = xid {
+        source_args.push(format!("xid={xid}"));
+    }
+
+    // X11 has no leaked fd to clean up, so the post-spawn hook is a no-op.
+    pipeline::spawn(opts, quality, source_dims, source_args, || {}).await
+}
+
+/// Run `xwininfo` and let the user click the window they want to share, then
+/// parse the `Window id: 0x…` line out of its output. Returns the numeric XID.
+async fn pick_window() -> Result<u32> {
+    eprintln!("[pixelpass] click the window you want to share…");
+    let output = Command::new("xwininfo")
+        .output()
+        .await
+        .context("failed to run `xwininfo` (install xorg-xwininfo)")?;
+    if !output.status.success() {
+        bail!(
+            "xwininfo failed: {}",
+            String::from_utf8_lossy(&output.stderr).trim()
+        );
+    }
+    let text = String::from_utf8_lossy(&output.stdout);
+    for line in text.lines() {
+        // e.g.  "xwininfo: Window id: 0x3a00007 \"xterm\""
+        if let Some((_, rest)) = line.split_once("Window id: ") {
+            let token = rest.split_whitespace().next().unwrap_or("");
+            let hex = token.strip_prefix("0x").unwrap_or(token);
+            if let Ok(xid) = u32::from_str_radix(hex, 16) {
+                return Ok(xid);
+            }
+        }
+    }
+    bail!("could not parse a window id from xwininfo output");
+}
+
+/// Read pixel dimensions: the selected window's geometry when `--window` was
+/// used, otherwise the root window of the screen named by `$DISPLAY`.
+fn read_geometry(xid: Option<u32>) -> Result<(u16, u16)> {
+    let (conn, screen_num) =
+        x11rb::connect(None).context("could not connect to the X server (is DISPLAY set?)")?;
+    match xid {
+        Some(id) => {
+            let geo = conn
+                .get_geometry(id)
+                .context("GetGeometry request failed")?
+                .reply()
+                .context("GetGeometry reply failed")?;
+            Ok((geo.width, geo.height))
+        }
+        None => {
+            let screen = &conn.setup().roots[screen_num];
+            Ok((screen.width_in_pixels, screen.height_in_pixels))
+        }
+    }
+}

src/interactive.rs

@@ -3,7 +3,8 @@ use dialoguer::{Input, Select, theme::ColorfulTheme};
 use iroh_tickets::endpoint::EndpointTicket;
 use std::str::FromStr;
 
-use crate::cli::Cli;
+use crate::cli::{Cli, Quality};
+use crate::common::{bandwidth, config};
 use crate::{host, viewer};
 
 pub async fn run(cli: Cli) -> Result<()> {
@@ -20,7 +21,17 @@ pub async fn run(cli: Cli) -> Result<()> {
         .interact()?;
 
     match choice {
-        0 => host::run(cli.into_host_opts(true)).await,
+        0 => {
+            preflight_if_needed(&theme).await;
+            let mut cli = cli;
+            if cli.app.is_none() {
+                cli.app = pick_app(&theme)?;
+            }
+            if cli.quality.is_none() {
+                cli.quality = Some(pick_quality(&theme)?);
+            }
+            host::run(cli.into_host_opts(true)).await
+        }
         _ => {
             let ticket = prompt_ticket(&theme)?;
             viewer::run(ticket, cli.into_viewer_opts(true)).await
@@ -28,6 +39,218 @@ pub async fn run(cli: Cli) -> Result<()> {
     }
 }
 
+/// Picker for the per-app audio capture choice. Lists apps currently
+/// producing audio (deduped by `application.name`); user picks one or
+/// the "all system audio" default. Bypassed when `--app NAME` was given
+/// on the CLI.
+fn pick_app(theme: &ColorfulTheme) -> Result<Option<String>> {
+    let apps = match host::audio::list_playing_apps() {
+        Ok(a) => a,
+        Err(e) => {
+            tracing::warn!("could not enumerate playing apps: {e:#}");
+            return Ok(None);
+        }
+    };
+
+    eprintln!();
+    eprintln!("Audio capture");
+    eprintln!("─────────────");
+    if apps.is_empty() {
+        eprintln!("No other apps are currently producing audio.");
+        eprintln!("Start your game / music / call first if you want to pick it specifically.");
+    }
+    eprintln!();
+
+    let mut items = vec!["Capture all system audio (default)".to_string()];
+    for app in &apps {
+        items.push(if app.stream_count == 1 {
+            app.name.clone()
+        } else {
+            format!("{} ({} streams)", app.name, app.stream_count)
+        });
+    }
+
+    let choice = Select::with_theme(theme)
+        .with_prompt("What audio should the viewer hear?")
+        .items(&items)
+        .default(0)
+        .interact()?;
+
+    if choice == 0 {
+        Ok(None)
+    } else {
+        Ok(Some(apps[choice - 1].name.clone()))
+    }
+}
+
+/// Picker for the encode quality preset. Mirrors [`pick_app`]; bypassed when
+/// `--quality` was given on the CLI. Quality is host-global (the same stream
+/// fans out to every viewer), so this is the one choice that sets it for all.
+fn pick_quality(theme: &ColorfulTheme) -> Result<Quality> {
+    eprintln!();
+    eprintln!("Quality");
+    eprintln!("───────");
+    eprintln!("Lower presets trade resolution + bitrate for less upload usage.");
+    eprintln!("The same quality is sent to every viewer.");
+    eprintln!();
+
+    // Order mirrors the labels below; index maps back to a Quality.
+    let choices = [
+        Quality::Auto,
+        Quality::Source,
+        Quality::High,
+        Quality::Medium,
+        Quality::Low,
+    ];
+    let items = [
+        "Auto — pick from my measured upstream (recommended)",
+        "Source — native resolution, 6000 kbps",
+        "High — up to 1080p, 4000 kbps",
+        "Medium — up to 720p, 2500 kbps",
+        "Low — up to 480p, 1000 kbps",
+    ];
+
+    let choice = Select::with_theme(theme)
+        .with_prompt("What quality should the viewer(s) get?")
+        .items(&items)
+        .default(0)
+        .interact()?;
+
+    Ok(choices[choice])
+}
+
+/// `pixelpass --reconfigure` entry point: unconditionally re-run the
+/// bandwidth pre-flight test, save the result, and return. Used to
+/// refresh a stale measurement (e.g. user moved house, changed ISP).
+pub async fn run_reconfigure() -> Result<()> {
+    eprintln!();
+    eprintln!("Re-running bandwidth pre-flight test…");
+    let mut cfg = config::load().unwrap_or_default();
+    run_bandwidth_test(&mut cfg).await;
+    Ok(())
+}
+
+/// First-run pre-flight gate. Called once, when the user picks "Host" in
+/// the interactive menu. Behavior by saved status:
+/// - Unmeasured (first ever launch): explain + offer Run / Skip
+/// - Failed (previous attempt errored): offer Retry / give-up-and-skip
+/// - Measured or Skipped: silent — never re-prompts
+async fn preflight_if_needed(theme: &ColorfulTheme) {
+    let mut cfg = config::load().unwrap_or_default();
+    match cfg.bandwidth.status {
+        config::BandwidthStatus::Measured | config::BandwidthStatus::Skipped => return,
+        config::BandwidthStatus::Unmeasured => {
+            eprintln!();
+            eprintln!("First-time setup");
+            eprintln!("────────────────");
+            eprintln!("PixelPass can measure your upload speed to recommend a safe");
+            eprintln!("default for how many viewers your connection can handle.");
+            eprintln!("The test takes about 5 seconds and uploads ~5 MB to");
+            eprintln!("Cloudflare's open speed-test endpoint.");
+            eprintln!();
+            eprintln!("If you skip, a conservative default (2 viewers) is used.");
+            eprintln!("You can run the test later with `pixelpass --reconfigure`.");
+            eprintln!();
+
+            let Ok(choice) = Select::with_theme(theme)
+                .with_prompt("What would you like to do?")
+                .items(&[
+                    "Run the bandwidth test (recommended)",
+                    "Skip — use the conservative default",
+                ])
+                .default(0)
+                .interact()
+            else {
+                return;
+            };
+
+            if choice == 1 {
+                cfg.bandwidth = config::BandwidthEntry {
+                    status: config::BandwidthStatus::Skipped,
+                    upstream_mbps: None,
+                    measured_at: None,
+                };
+                let _ = config::save(&cfg);
+                eprintln!("Pre-flight skipped.");
+                return;
+            }
+            run_bandwidth_test(&mut cfg).await;
+        }
+        config::BandwidthStatus::Failed => {
+            eprintln!();
+            let Ok(choice) = Select::with_theme(theme)
+                .with_prompt("Last bandwidth test failed. Try again?")
+                .items(&[
+                    "Yes — retry now",
+                    "No — use the conservative default",
+                ])
+                .default(0)
+                .interact()
+            else {
+                return;
+            };
+
+            if choice == 1 {
+                cfg.bandwidth = config::BandwidthEntry {
+                    status: config::BandwidthStatus::Skipped,
+                    upstream_mbps: None,
+                    measured_at: None,
+                };
+                let _ = config::save(&cfg);
+                eprintln!("OK — using the conservative default.");
+                return;
+            }
+            run_bandwidth_test(&mut cfg).await;
+        }
+    }
+}
+
+async fn run_bandwidth_test(cfg: &mut config::Config) {
+    eprintln!();
+    eprintln!("Measuring upstream…");
+
+    let result = tokio::task::spawn_blocking(bandwidth::measure_upstream_blocking).await;
+    let measurement = match result {
+        Ok(Ok(m)) => m,
+        Ok(Err(e)) => {
+            eprintln!("Test failed: {e:#}");
+            eprintln!("Marking as failed — you'll be asked again on next launch.");
+            cfg.bandwidth = config::BandwidthEntry {
+                status: config::BandwidthStatus::Failed,
+                upstream_mbps: None,
+                measured_at: None,
+            };
+            let _ = config::save(cfg);
+            return;
+        }
+        Err(join_err) => {
+            eprintln!("Test task panicked: {join_err}");
+            cfg.bandwidth = config::BandwidthEntry {
+                status: config::BandwidthStatus::Failed,
+                upstream_mbps: None,
+                measured_at: None,
+            };
+            let _ = config::save(cfg);
+            return;
+        }
+    };
+
+    eprintln!(
+        "Measured {:.2} Mbps up (safe estimate {:.2} Mbps, took {:.1}s).",
+        measurement.raw_mbps,
+        measurement.safe_mbps,
+        measurement.elapsed.as_secs_f64()
+    );
+    cfg.bandwidth = config::BandwidthEntry {
+        status: config::BandwidthStatus::Measured,
+        upstream_mbps: Some(measurement.safe_mbps),
+        measured_at: Some(chrono::Utc::now()),
+    };
+    if let Err(e) = config::save(cfg) {
+        eprintln!("Warning: failed to save result: {e:#}");
+    }
+}
+
 fn print_welcome() {
     eprintln!();
     eprintln!("Welcome to PixelPass.");
@@ -68,14 +291,52 @@ impl Player {
                     url,
                 ],
             ),
-            Player::Vlc => crate::common::process::spawn_detached(
-                "vlc",
-                &["--network-caching=200", "--live-caching=200", url],
-            ),
+            Player::Vlc => {
+                warn_if_vlc_plugins_missing();
+                crate::common::process::spawn_detached(
+                    "vlc",
+                    &["--network-caching=200", "--live-caching=200", url],
+                )
+            }
         }
     }
 }
 
+// On Arch-family distros, the base `vlc` package omits two plugins
+// pixelpass needs: the MPEG-TS demuxer (`vlc-plugin-dvb`) and the
+// libavcodec-based H.264 decoder (`vlc-plugin-ffmpeg`). Missing either
+// produces a confusing error chain — warn at launch.
+fn warn_if_vlc_plugins_missing() {
+    const REQUIRED: &[(&str, &str)] = &[
+        (
+            "/usr/lib/vlc/plugins/demux/libts_plugin.so",
+            "vlc-plugin-dvb",
+        ),
+        (
+            "/usr/lib/vlc/plugins/codec/libavcodec_plugin.so",
+            "vlc-plugin-ffmpeg",
+        ),
+    ];
+    let missing: Vec<&(&str, &str)> = REQUIRED
+        .iter()
+        .filter(|(p, _)| !std::path::Path::new(p).exists())
+        .collect();
+    if missing.is_empty() {
+        return;
+    }
+    eprintln!();
+    eprintln!("Warning: VLC is missing plugins pixelpass needs:");
+    for (path, pkg) in &missing {
+        eprintln!("  - {path} (install `{pkg}`)");
+    }
+    eprintln!("On Arch / CachyOS / EndeavourOS: `sudo pacman -S {}`.", {
+        let names: Vec<&str> = missing.iter().map(|(_, p)| *p).collect();
+        names.join(" ")
+    });
+    eprintln!("mpv is unaffected.");
+    eprintln!();
+}
+
 pub fn prompt_player() -> Result<Player> {
     let theme = ColorfulTheme::default();
     let choice = Select::with_theme(&theme)

src/main.rs

@@ -1,5 +1,7 @@
 mod cli;
 mod common;
+#[cfg(feature = "gui")]
+mod gui;
 mod host;
 mod interactive;
 mod repair;
@@ -16,10 +18,46 @@ async fn main() -> Result<()> {
     let cli = Cli::parse();
     init_tracing(cli.verbose);
 
+    if matches!(cli.output, Some(cli::OutputFormat::Json)) {
+        common::output::set_json(true);
+    }
+
+    if cli.gui {
+        #[cfg(feature = "gui")]
+        {
+            return gui::run();
+        }
+        #[cfg(not(feature = "gui"))]
+        {
+            anyhow::bail!(
+                "this binary was built without GUI support. Rebuild with \
+                 `cargo build --release --features gui` to use --gui."
+            );
+        }
+    }
+
+    // libpipewire requires global init before any pw_* call. Idempotent;
+    // safe to call even when the per-app audio thread never spawns.
+    pipewire::init();
+
     if cli.repair {
         return repair::run().await;
     }
 
+    if cli.reconfigure {
+        return interactive::run_reconfigure().await;
+    }
+
+    if cli.host {
+        if cli.ticket.is_some() {
+            anyhow::bail!(
+                "--host and a ticket argument are mutually exclusive: --host shares your \
+                 screen, a ticket views someone else's."
+            );
+        }
+        return host::run(cli.into_host_opts(false)).await;
+    }
+
     match cli.ticket.as_deref() {
         Some(s) => {
             let ticket: EndpointTicket = s.parse().map_err(|e| {
@@ -37,5 +75,14 @@ async fn main() -> Result<()> {
 fn init_tracing(verbose: bool) {
     let default = if verbose { "pixelpass=trace,iroh=info" } else { "pixelpass=info,iroh=warn" };
     let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new(default));
-    tracing_subscriber::fmt().with_env_filter(filter).with_target(false).init();
+    // Tracing MUST write to stderr. `tracing_subscriber::fmt()` defaults its
+    // writer to stdout, but with `--output json` stdout carries the JSON event
+    // stream the `--gui` front-end parses (see `common::output`) — logging there
+    // interleaves log lines into that stream (corrupting events and starving the
+    // GUI's stderr-tail diagnostics). Pin it to stderr to honor that contract.
+    tracing_subscriber::fmt()
+        .with_writer(std::io::stderr)
+        .with_env_filter(filter)
+        .with_target(false)
+        .init();
 }

src/repair.rs

@@ -1,12 +1,197 @@
-//! `--repair`: clean up any null sinks / loopbacks that a crashed pixelpass
-//! host left behind. Phase 2 will scan PipeWire for nodes tagged with the
-//! `pixelpass.session = <uuid>` property and destroy them.
+//! `--repair`: clean up null-sinks and loopbacks left behind by a crashed
+//! pixelpass host. Identifies orphans by the `pixelpass_capture_<pid>`
+//! name pattern + dead-PID check, then unloads paired loopbacks first
+//! (mirrors `Routing::shutdown`'s order so PipeWire doesn't leave zombie
+//! links). Live PIDs — including this process and any other running
+//! pixelpass — are left alone.
 
-use anyhow::Result;
+use anyhow::{Context, Result, bail};
+use std::collections::HashSet;
+use std::path::Path;
+use std::process::Command;
+
+const SINK_NAME_PREFIX: &str = "pixelpass_capture_";
 
 pub async fn run() -> Result<()> {
-    eprintln!("[pixelpass] --repair: PipeWire scan not yet implemented (Phase 2).");
-    eprintln!("            Run `pactl list short sinks | grep pixelpass` to spot orphans,");
-    eprintln!("            and `pactl unload-module <id>` to remove them manually.");
+    let modules = list_modules().context("failed to list pactl modules")?;
+
+    let mut dead_sinks: Vec<OrphanSink> = Vec::new();
+    let mut dead_pids: HashSet<u32> = HashSet::new();
+    let mut live_skipped: u32 = 0;
+
+    for m in &modules {
+        if m.name != "module-null-sink" {
+            continue;
+        }
+        let Some(sink_name) = extract_kv(&m.args, "sink_name") else {
+            continue;
+        };
+        let Some(pid_str) = sink_name.strip_prefix(SINK_NAME_PREFIX) else {
+            continue;
+        };
+        let Ok(pid) = pid_str.parse::<u32>() else {
+            continue;
+        };
+
+        if is_pid_alive(pid) {
+            live_skipped += 1;
+            continue;
+        }
+        dead_pids.insert(pid);
+        dead_sinks.push(OrphanSink {
+            id: m.id,
+            sink_name: sink_name.to_string(),
+            pid,
+        });
+    }
+
+    let mut dead_loopbacks: Vec<u32> = Vec::new();
+    for m in &modules {
+        if m.name != "module-loopback" {
+            continue;
+        }
+        let Some(sink) = extract_kv(&m.args, "sink") else {
+            continue;
+        };
+        let Some(pid_str) = sink.strip_prefix(SINK_NAME_PREFIX) else {
+            continue;
+        };
+        let Ok(pid) = pid_str.parse::<u32>() else {
+            continue;
+        };
+        if dead_pids.contains(&pid) {
+            dead_loopbacks.push(m.id);
+        }
+    }
+
+    if dead_sinks.is_empty() && dead_loopbacks.is_empty() {
+        if live_skipped > 0 {
+            println!(
+                "[pixelpass] --repair: nothing to clean up ({live_skipped} live pixelpass host(s) left alone)."
+            );
+        } else {
+            println!("[pixelpass] --repair: nothing to clean up.");
+        }
+        return Ok(());
+    }
+
+    let mut unloaded = 0u32;
+    let mut failed = 0u32;
+
+    for id in &dead_loopbacks {
+        match unload_module(*id) {
+            Ok(()) => {
+                println!("[pixelpass] --repair: unloaded loopback module #{id}");
+                unloaded += 1;
+            }
+            Err(e) => {
+                eprintln!("[pixelpass] --repair: failed to unload loopback #{id}: {e:#}");
+                failed += 1;
+            }
+        }
+    }
+    for orphan in &dead_sinks {
+        match unload_module(orphan.id) {
+            Ok(()) => {
+                println!(
+                    "[pixelpass] --repair: unloaded {} (orphaned from pid {})",
+                    orphan.sink_name, orphan.pid
+                );
+                unloaded += 1;
+            }
+            Err(e) => {
+                eprintln!(
+                    "[pixelpass] --repair: failed to unload {} (#{}): {e:#}",
+                    orphan.sink_name, orphan.id
+                );
+                failed += 1;
+            }
+        }
+    }
+
+    if live_skipped > 0 {
+        println!(
+            "[pixelpass] --repair: left {live_skipped} live pixelpass host(s) alone."
+        );
+    }
+
+    if failed > 0 {
+        bail!("--repair: {failed} module(s) failed to unload (see errors above)");
+    }
+    println!("[pixelpass] --repair: cleaned up {unloaded} module(s).");
+    Ok(())
+}
+
+struct Module {
+    id: u32,
+    name: String,
+    args: String,
+}
+
+struct OrphanSink {
+    id: u32,
+    sink_name: String,
+    pid: u32,
+}
+
+fn list_modules() -> Result<Vec<Module>> {
+    let output = Command::new("pactl")
+        .args(["list", "short", "modules"])
+        .output()
+        .context("failed to run `pactl list short modules`")?;
+    if !output.status.success() {
+        bail!(
+            "pactl list short modules failed: {}",
+            String::from_utf8_lossy(&output.stderr).trim()
+        );
+    }
+    let text = String::from_utf8(output.stdout).context("pactl returned non-UTF-8")?;
+    let mut modules = Vec::new();
+    // `pactl list short modules` is tab-separated, but some modules have
+    // multi-line `{ ... }` argument blocks that wrap onto continuation
+    // lines starting with whitespace. The wrap lines never parse as a
+    // u32 ID, so the simple per-line + parse-id filter is robust.
+    for line in text.lines() {
+        let mut parts = line.splitn(4, '\t');
+        let Some(id_str) = parts.next() else { continue };
+        let Ok(id) = id_str.parse::<u32>() else { continue };
+        let Some(name) = parts.next() else { continue };
+        let args = parts.next().unwrap_or("").to_string();
+        modules.push(Module {
+            id,
+            name: name.to_string(),
+            args,
+        });
+    }
+    Ok(modules)
+}
+
+fn extract_kv<'a>(args: &'a str, key: &str) -> Option<&'a str> {
+    for token in args.split_whitespace() {
+        if let Some(rest) = token.strip_prefix(key)
+            && let Some(value) = rest.strip_prefix('=')
+        {
+            return Some(value);
+        }
+    }
+    None
+}
+
+fn is_pid_alive(pid: u32) -> bool {
+    Path::new(&format!("/proc/{pid}")).exists()
+}
+
+fn unload_module(id: u32) -> Result<()> {
+    let output = Command::new("pactl")
+        .arg("unload-module")
+        .arg(id.to_string())
+        .output()
+        .context("failed to run pactl unload-module")?;
+    if !output.status.success() {
+        bail!(
+            "pactl unload-module #{id}: {}",
+            String::from_utf8_lossy(&output.stderr).trim()
+        );
+    }
     Ok(())
 }

src/viewer/mod.rs

@@ -1,11 +1,18 @@
-use anyhow::{Context, Result};
+use anyhow::{Context, Result, bail};
 use iroh::Endpoint;
 use iroh::endpoint::presets;
 use iroh_tickets::endpoint::EndpointTicket;
+use std::time::Duration;
 use tokio::net::TcpListener;
 
 use crate::cli::ViewerOpts;
-use crate::common::{alpn::ALPN, signal};
+use crate::common::{alpn::ALPN, output, signal};
+
+/// Cap on the initial QUIC connect. `endpoint.connect()` has no built-in
+/// deadline, so an offline host / stale code / unreachable relay otherwise
+/// hangs forever with no feedback (the silent "connecting…" failure mode).
+/// Matches the host's 15s `online()` cap.
+const CONNECT_TIMEOUT: Duration = Duration::from_secs(15);
 
 pub async fn run(ticket: EndpointTicket, opts: ViewerOpts) -> Result<()> {
     let cancel = signal::install_ctrl_c();
@@ -17,12 +24,38 @@ pub async fn run(ticket: EndpointTicket, opts: ViewerOpts) -> Result<()> {
 
     let addr = ticket.endpoint_addr().clone();
     tracing::info!(remote = %addr.id, "connecting to host");
-    let conn = endpoint.connect(addr, ALPN).await?;
+
+    // Bound the connect attempt and let ctrl-c abort it, so the viewer fails
+    // loud (and the GUI surfaces the error) instead of spinning indefinitely.
+    let conn = tokio::select! {
+        _ = cancel.cancelled() => {
+            tracing::info!("ctrl-c received before the connection was established");
+            endpoint.close().await;
+            return Ok(());
+        }
+        result = tokio::time::timeout(CONNECT_TIMEOUT, endpoint.connect(addr, ALPN)) => match result {
+            Ok(Ok(conn)) => conn,
+            Ok(Err(e)) => {
+                endpoint.close().await;
+                bail!("failed to connect to the host: {e:#}");
+            }
+            Err(_) => {
+                endpoint.close().await;
+                bail!(
+                    "couldn't reach the host within {}s — it may be offline, the share \
+                     code may be stale, or the relay may be unreachable. Check that the \
+                     host is running, then re-copy the code and try again.",
+                    CONNECT_TIMEOUT.as_secs()
+                );
+            }
+        },
+    };
     let (quic_send, quic_recv) = conn.open_bi().await?;
 
     let listener = TcpListener::bind(("127.0.0.1", opts.port)).await?;
     let port = listener.local_addr()?.port();
     let url = format!("http://127.0.0.1:{port}");
+    output::emit(output::Event::Connected { url: &url });
 
     if opts.interactive {
         let player = crate::interactive::prompt_player()?;