host/x11: default to XDamage capture; drop --untimed from viewers

X11 full-desktop capture used `ximagesrc use-damage=false`, which copies
the whole root window every frame. On servers without working MIT-SHM
(and CPU-bound everywhere else) this collapses to ~1 fps — a field test
over an xlibre host played back at roughly one frame per minute. Default
to `use-damage=true` (XDamage re-grabs only changed regions); keep
`PIXELPASS_X11_NO_DAMAGE=1` as an escape hatch for driver artifacts.

Also drop `--untimed` from both mpv invocations (viewer banner + the
interactive launcher). `--untimed` displays each frame as it decodes and
ignores audio timestamps, which drifts a shared *video* progressively
out of sync with its audio. Pacing to the audio clock keeps A/V synced
at a negligible latency cost.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/host/audio.rs

@@ -280,7 +280,9 @@ impl Drop for Routing {
 /// initial `lost`. In every other mode (whole-desktop, or best-effort app
 /// filtering) the loopback keeps audio flowing from the outset, so there is no
 /// initial gap to report. Pure: no I/O, so the emit decision is unit-testable.
-pub(super) fn initial_app_audio_state(opts: &HostOpts) -> Option<crate::common::output::AppAudioState> {
+pub(super) fn initial_app_audio_state(
+    opts: &HostOpts,
+) -> Option<crate::common::output::AppAudioState> {
     (opts.app.is_some() && opts.strict_audio).then_some(crate::common::output::AppAudioState::Lost)
 }
 

src/host/mod.rs

@@ -523,7 +523,10 @@ mod tests {
 
     #[test]
     fn capture_summary_reflects_audio_mode() {
-        assert_eq!(capture_summary(&opts(None, false)), "fullscreen + system-audio");
+        assert_eq!(
+            capture_summary(&opts(None, false)),
+            "fullscreen + system-audio"
+        );
         assert_eq!(
             capture_summary(&opts(Some("Firefox"), false)),
             "fullscreen + app-audio=Firefox"
@@ -533,7 +536,10 @@ mod tests {
             capture_summary(&opts(Some("Firefox"), true)),
             "fullscreen + app-audio=Firefox (strict)"
         );
-        assert_eq!(capture_summary(&opts(None, true)), "fullscreen + system-audio");
+        assert_eq!(
+            capture_summary(&opts(None, true)),
+            "fullscreen + system-audio"
+        );
     }
 
     #[test]

src/host/x11.rs

@@ -37,12 +37,22 @@ pub async fn start(opts: &HostOpts, quality: &EffectiveQuality) -> Result<Captur
         }
     };
 
+    // XDamage capture (`use-damage=true`) only re-grabs changed screen
+    // regions instead of copying the whole root window every frame. On a busy
+    // desktop that is the difference between a usable framerate and ~1 fps —
+    // `use-damage=false` does a full XGetImage per frame, which collapses on
+    // servers without working MIT-SHM (and pins the CPU everywhere else).
+    // Kept as the default; `PIXELPASS_X11_NO_DAMAGE=1` restores full-frame
+    // capture if a driver produces partial-update artifacts with damage on.
+    let use_damage = if std::env::var_os("PIXELPASS_X11_NO_DAMAGE").is_some() {
+        "use-damage=false"
+    } else {
+        "use-damage=true"
+    };
     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 matches Wayland's CursorMode::Embedded.
+        use_damage.to_string(),
         "show-pointer=true".to_string(),
     ];
     if let Some(xid) = xid {

src/interactive.rs

@@ -279,8 +279,9 @@ impl Player {
             Player::Mpv => crate::common::process::spawn_detached(
                 "mpv",
                 &[
+                    // No `--untimed`: it ignores audio timestamps and drifts a
+                    // shared video out of sync. Pacing to audio keeps A/V synced.
                     "--profile=low-latency",
-                    "--untimed",
                     "--hwdec=auto",
                     "--audio-buffer=0.2",
                     "--demuxer-max-bytes=2M",

src/repair.rs

@@ -172,7 +172,9 @@ fn loopback_capture_pid(args: &str) -> Option<u32> {
     let from_source = extract_kv(args, "source")
         .and_then(|v| v.strip_prefix(SINK_NAME_PREFIX))
         .and_then(|rest| rest.strip_suffix(".monitor"));
-    from_sink.or(from_source).and_then(|pid| pid.parse::<u32>().ok())
+    from_sink
+        .or(from_source)
+        .and_then(|pid| pid.parse::<u32>().ok())
 }
 
 fn extract_kv<'a>(args: &'a str, key: &str) -> Option<&'a str> {

src/viewer/mod.rs

@@ -102,7 +102,7 @@ fn print_viewer_banner(url: &str) {
     eprintln!("│  Connected to host. Open the stream in your player:");
     eprintln!("│");
     eprintln!(
-        "│    mpv --profile=low-latency --untimed --hwdec=auto --audio-buffer=0.2 --demuxer-max-bytes=2M --demuxer-readahead-secs=0.5 {url}"
+        "│    mpv --profile=low-latency --hwdec=auto --audio-buffer=0.2 --demuxer-max-bytes=2M --demuxer-readahead-secs=0.5 {url}"
     );
     eprintln!("│    vlc --network-caching=200 --live-caching=200 {url}");
     eprintln!("│");