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zebra-spaces: bump playoutDelayHint 400ms -> 700ms for cross-Wi-Fi voice

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Reports of robot-voice artifacts from a peer on a different Wi-Fi —
classic symptom of jitter-buffer under-runs (Opus PLC kicks in,
generates synthetic samples that sound vocoder-y). 400ms was tight
enough that bursty inter-arrival on cross-AP / cellular hand-off
networks would exhaust the cushion.

700ms costs barely-audible end-to-end latency (well under the 1s
people perceive as 'walkie talkie'), well above typical Wi-Fi peak
jitter, and matches both the SFU subscribe path and mesh peer path
so the room sounds consistent regardless of how the audio is being
delivered.

Bitrate / FEC / DTX settings unchanged — adding bandwidth would
make a lossy link worse, not better.
This commit is contained in:
Russell Ballestrini 2026-06-03 13:19:38 -04:00
parent 79ee317ccf
commit 1920cf6a55
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1 changed files with 12 additions and 7 deletions
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19
web/zebra-spaces.html
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@ -2523,8 +2523,12 @@ function handleRemoteSfuTrack(ev){
logLine('', 'sfu: unknown kind '+kind+' from '+pubHex);
return;
}
/* mic audio — 400ms jitter-buffer target absorbs Wi-Fi peak jitter */
try { if (ev.receiver) ev.receiver.playoutDelayHint = 0.4; } catch(_){}
/* mic audio — 700ms jitter-buffer target absorbs cross-Wi-Fi peak
* jitter and burst packet loss. 400ms was too tight for users on
* different APs / cellular hand-offs — under-runs were producing
* the 'robot voice' artifact. 700ms costs an inaudible bit of
* end-to-end latency in exchange for clean playback under loss. */
try { if (ev.receiver) ev.receiver.playoutDelayHint = 0.7; } catch(_){}
/* cache by full pubkey (already resolved above) so it survives the
* member's session uuid changing across leave/rejoin */
sfuStreamsByPubHex.set(pubHex, ev.streams[0]);
@ -3494,9 +3498,10 @@ async function connectToPeer(uuid, weOffer){
let a = remoteAudio.get(uuid);
if (!a){ a = document.createElement('audio'); a.autoplay = true; document.body.appendChild(a); remoteAudio.set(uuid, a); }
a.srcObject = ev.streams[0] || new MediaStream([ev.track]);
/* 400ms jitter buffer — Wi-Fi peak inter-arrival is multiples of
* the smoothed jitter, so a generous buffer absorbs the bursts */
try { ev.receiver.playoutDelayHint = 0.4; } catch(_){}
/* 700ms jitter buffer — matches the SFU path. Cross-Wi-Fi and
* cellular hand-off jitter ate into the old 400ms cushion and
* produced robot-voice artifacts on tighter networks. */
try { ev.receiver.playoutDelayHint = 0.7; } catch(_){}
stopMeter(uuid); startMeter(uuid, a.srcObject);
};
pc.onicecandidate = (ev) => { /* using waitForIceGathering pattern, candidates ignored */ };
@ -4086,8 +4091,8 @@ logLine('', 'ready — pick a handle, type a rendezvous code, enter the space');
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