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zebra-report: force G.711/G.722 codec (fix amplitude modem over WebRTC)

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russell@unturf.com 2026-05-28 10:51:57 -04:00
parent c234cb9055
commit e3340a776b
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zebra-report/index.html
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@ -1150,6 +1150,28 @@ function ensurePC() {
if (!carrierOn) throw new Error('start carrier first');
pc = new RTCPeerConnection(RTC_CONFIG);
for (const tr of outboundStream.getTracks()) pc.addTrack(tr, outboundStream);
/* Force a memoryless codec (G.711 PCMU/PCMA, else G.722) ahead of Opus.
* Opus is a perceptual codec that re-quantizes in 20ms frames and smears the
* MARK/SPACE bit-edges this modem rides on; G.711 companding is per-sample,
* preserving the carrier envelope like the PulseAudio path. */
try {
const caps = (RTCRtpSender.getCapabilities && RTCRtpSender.getCapabilities('audio')) || null;
if (caps && caps.codecs) {
const rank = (mime) => {
const m = (mime || '').toLowerCase();
if (m.endsWith('/pcmu')) return 0;
if (m.endsWith('/pcma')) return 1;
if (m.endsWith('/g722')) return 2;
if (m.includes('opus')) return 99;
return 50;
};
const ordered = caps.codecs.slice().sort((a, b) => rank(a.mimeType) - rank(b.mimeType));
for (const t of pc.getTransceivers()) {
if (t.setCodecPreferences) { try { t.setCodecPreferences(ordered); } catch (_) {} }
}
logLine('sys', 'codec preference: G.711/G.722 ahead of Opus (clean amplitude)');
}
} catch (_) {}
pc.ontrack = (ev) => {
const stream = ev.streams[0] || new MediaStream([ev.track]);
attachInboundTrack(stream, ev.track.id);