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fix(quality): scale after videoconvert at exact even WxH

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Live medium-quality stream errored with "negotiation problem" on the
host and rendered a squashed, garbled picture in the viewer. Two causes,
both from inserting videoscale before videoconvert with PAR+range caps:

- videoscale was scaling pipewiresrc's raw output directly. The portal
  source's format/memory (e.g. DMABuf) isn't something software videoscale
  negotiates — the original pipeline always fed pipewiresrc through
  videoconvert first. Move videoscale *after* videoconvert so it operates
  on system-memory NV12/I420.
- `pixel-aspect-ratio=1/1` + a width range over-constrained negotiation
  and risked a non-square-PAR / distorted result. Instead compute an exact
  even WxH from the known source dimensions (Wayland: portal size; X11:
  root/window geometry), preserving aspect, and pin it fully in the caps.
  This is also downscale-only now — a source already at/below the target
  height is left native instead of upscaled. Unknown dims (rare X11
  geometry failure) fall back to the height-only + square-pixel + even
  width-range negotiation.

source_dims threaded through pipeline::spawn from both backends. Smoke
test updated to mirror the new ordering (1920x1080 -> 852x480, videoscale
after videoconvert) and still asserts an even sub-source width.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
mollusk
2026-05-24 15:25:05 -04:00
co-authored by Claude Opus 4.7
parent 7483b9aae8
commit 8044a42f98
4 changed files with 69 additions and 42 deletions
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src/host/pipeline.rs
+43 -25
View File
@@ -66,17 +66,22 @@ impl Drop for CaptureHandle {
/// 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", …]`). `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.
/// …]` 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);
let args = build_args(&source_args, &audio_device, opts, quality, source_dims);
let mut gst_cmd = Command::new("gst-launch-1.0");
gst_cmd
@@ -148,6 +153,7 @@ fn build_args(
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();
@@ -187,9 +193,38 @@ fn build_args(
"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 => 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);
Some(format!("{raw_format},width={w},height={h}"))
}
Some(_) => None, // source already <= target height
None => 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.
// 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(),
@@ -197,26 +232,6 @@ fn build_args(
"!".into(),
framerate_caps,
"!".into(),
]);
// Optional downscale (quality presets). Omitted entirely for the native
// "Source" preset. `pixel-aspect-ratio=1/1` forces a *proportional* scale:
// screen capture always has square pixels, and without pinning PAR videoscale
// keeps the full source width and just squashes PAR to preserve display
// aspect (e.g. 1920x480 @ PAR 4/9 — no bandwidth win at all). With square
// pixels fixed, width follows the source DAR. H.264 4:2:0 needs even
// dimensions, so we pin height to an even value (preset heights already are;
// a raw --max-height override is rounded down) and constrain width to a
// stepped even range — verified 1920x1080→852x480 and 1366x768→1280x720.
if let Some(h) = quality.max_height {
let h = (h & !1).max(2);
args.extend([
"videoscale".into(),
"!".into(),
format!("video/x-raw,height={h},pixel-aspect-ratio=1/1,width=[2,8192,2]"),
"!".into(),
]);
}
args.extend([
"queue".into(),
"!".into(),
"videoconvert".into(),
@@ -224,6 +239,9 @@ fn build_args(
raw_format.into(),
"!".into(),
]);
if let Some(caps) = scale_caps {
args.extend(["videoscale".into(), "!".into(), caps, "!".into()]);
}
args.extend(encoder_args);
args.extend([
"!".into(),