Add README

Covers v0.1 status, quick-start (interactive + headless), system deps, build, architecture diagram, design rationale, and known limitations. No README existed before — this fills the gap now that v0.1 is verified. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-20 16:04:36 -04:00
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+# 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)
+- VAAPI H.264 encode in GStreamer (RDNA3 confirmed; other VAAPI-capable
+  GPUs should work)
+- Audio capture of the default sink's monitor
+- 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>`)
+
+Not yet working:
+- X11 capture (stubbed, returns an error)
+- Per-app audio routing (`--app <name>` is a flag stub)
+- Multi-viewer (single viewer per host by design right now)
+- VLC client renders the H.264 stream as a green screen — mpv works
+- `--repair` (PipeWire orphan cleanup) is a stub
+
+## 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).
+
+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
+```
+
+## Requirements
+
+- Linux (Wayland session for now; X11 stubbed)
+- 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`
+- PipeWire (for screencast portal + audio capture)
+
+On Arch / CachyOS:
+
+```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
+```
+
+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.
+
+## How it works
+
+```
+  Host                                                          Viewer
+  ────                                                          ──────
+  Wayland portal (ashpd) ──> PipeWire fd
+                              │
+                              ▼
+              gst-launch: pipewiresrc -> videorate -> vah264enc ->
+                          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
+hardware-encoded 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.
+
+## Known limitations and gotchas
+
+- **VLC shows a green screen** against a stream mpv handles correctly.
+  Likely a VLC-specific PCR / PMT / alignment expectation; not yet
+  diagnosed. Use mpv until this is fixed.
+- **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.
+- **Single viewer per host** by design right now. Restarting the player
+  against the same URL fails with "connection refused"; restart the
+  viewer too.
+- **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.