zebra-spaces: audio priority='high', video priority='low' at the RtpSender

When the sender's egress queue gets contended, audio wins. Fox 2026-06-04:
wiggling a terminal window (X11) caused 1-5s audio cutouts on all mesh
peers AND listeners — even with playoutDelayHint=4.0 on subs. Theory
(fox): "i might be the clients video trying to compete with the audio,
the wiggled updates" — exactly that. X11 window wiggling produced a
storm of dirty regions for screen-share; the encoder spiked into a big
keyframe burst; audio packets queued behind that burst arrived late;
listener's playoutDelayHint buffer drained.

Fix: RTCRtpEncodingParameters.priority + networkPriority. Set audio to
'high' (mic + any DJ audio track), video to 'low' (screen, camera).
Both Firefox and Chromium honor these for the local egress queue —
audio packets jump ahead of video bursts.

Applied at:
- setSenderBitrate (mic publisher) — high
- setSenderMaxBitrate (screen audio, camera audio) — high
- setSenderMaxBitrate (screen video, camera video) — low

No new param, no SDP renegotiation needed — setParameters() applies
immediately to the existing PC. Existing call sites all flow through
these two helpers, so the change reaches every publisher.

Pair with publisher-side outbound-rtp telemetry (836a036) — gap on
aud.send during a wiggle is now the metric we measure against.

web/zebra-spaces.html

@@ -3369,17 +3369,33 @@ async function setSenderBitrate(sender){
      * for speech. Opus VBR only spends what it needs; idle music stays around
      * 200–300 kbps and only peaks claim the ceiling. */
     p.encodings[0].maxBitrate = musicMode ? 256000 : 40000;
+    /* Audio rides ahead of video in the sender's egress queue. Fox
+     * 2026-06-04: wiggling a terminal window caused 1-5s cutouts on
+     * listeners even with a 4s playoutDelayHint buffer. Cause: the
+     * wiggle triggered a big screen-share keyframe burst that
+     * monopolized the egress queue; audio packets queued behind it
+     * arrived too late and the buffer drained. Setting priority='high'
+     * + networkPriority='high' on audio tells the browser to drain
+     * audio first when its outgoing queue is contended. Video keeps
+     * the default ('low' on the screen/camera senders below). */
+    p.encodings[0].priority = 'high';
+    p.encodings[0].networkPriority = 'high';
     await sender.setParameters(p);
   } catch(_){}
 }
 /* explicit bitrate setter for non-mic senders (screen video, screen audio).
- * setSenderBitrate above is locked to the mic's musicMode value. */
+ * setSenderBitrate above is locked to the mic's musicMode value. Audio kind
+ * gets high priority like the mic; video kind gets low priority so audio
+ * wins the egress queue under contention. */
 async function setSenderMaxBitrate(sender, bps){
   if (!sender) return;
   try {
     const p = sender.getParameters();
     if (!p.encodings || !p.encodings.length) p.encodings = [{}];
     p.encodings[0].maxBitrate = bps;
+    const isVideo = sender.track && sender.track.kind === 'video';
+    p.encodings[0].priority        = isVideo ? 'low'    : 'high';
+    p.encodings[0].networkPriority = isVideo ? 'low'    : 'high';
     await sender.setParameters(p);
   } catch(_){}
 }
@@ -5925,8 +5941,8 @@ logLine('', 'ready — pick a handle, type a rendezvous code, enter the space');
 
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