WebRTC audio mirror: AAC cannot cross WebRTC, so transcode audio to Opus into <path>.webrtc

bin/mtx-on-ready.sh (runOnReady inside the mediamtx container) posts the is-live notice and, for sources whose
audio is not Opus, runs ffmpeg: video copy, audio -> Opus, published over MediaMTX's loopback RTSP to
<user>/<Title>.webrtc (record: no). dumpd accepts .webrtc publishes only from 127.0.0.1. The portal hides
mirror paths, plays the mirror over WHEP (HLS stays on the source), holds an AAC source for 15 s while its
mirror comes up, and corrects the viewer count. Verified headless with a mocked path list.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

live/src/Player.jsx

@@ -6,6 +6,7 @@ import { audio, effectiveMuted } from './useAudio.js'
 // WebRTC (WHEP) first, HLS fallback. Mute/volume come from the shared audio store.
 export default function Player({ params, api }) {
   const { id, user, title } = params
+  const whep = params.whep || id                       // Opus audio mirror path when the source audio is AAC
   const videoRef = useRef(null)
   const [status, setStatus] = useState('connecting…')
   const [viewers, setViewers] = useState(params.viewers ?? 0)
@@ -78,7 +79,7 @@ export default function Player({ params, api }) {
         const offer = await pc.createOffer()
         await pc.setLocalDescription(offer)
         await new Promise(res => { if (pc.iceGatheringState === 'complete') return res(); const t = setTimeout(res, 1500); pc.onicegatheringstatechange = () => { if (pc.iceGatheringState === 'complete') { clearTimeout(t); res() } } })
-        const r = await fetch(whepUrl(id), { method: 'POST', headers: { 'Content-Type': 'application/sdp' }, body: pc.localDescription.sdp, credentials: 'same-origin' })
+        const r = await fetch(whepUrl(whep), { method: 'POST', headers: { 'Content-Type': 'application/sdp' }, body: pc.localDescription.sdp, credentials: 'same-origin' })
         if (!r.ok) throw new Error('whep ' + r.status)
         await pc.setRemoteDescription({ type: 'answer', sdp: await r.text() })
         setStatus('webrtc')
@@ -90,7 +91,7 @@ export default function Player({ params, api }) {
     }
     startWhep()
     return () => { cancelled = true; try { pc?.close() } catch {}; try { hls?.destroy() } catch {}; v.srcObject = null; v.removeAttribute('src') }
-  }, [id])
+  }, [id, whep])
 
   const icon = muted ? '🔇' : volume === 0 ? '🔈' : volume < 0.5 ? '🔉' : '🔊'
   return (

live/src/api.js

@@ -1,22 +1,37 @@
 // MediaMTX control API, proxied by Caddy at /api (-> 127.0.0.1:9997). Returns active streams.
+const VIDEO = new Set(['H264', 'H265', 'VP8', 'VP9', 'AV1', 'MJPEG', 'M-JPEG', 'MPEG-4 Video', 'MPEG-1 Video'])
+const firstSeen = new Map()                      // path -> first time we saw it ready (mirror grace period)
+const MIRROR_WAIT_MS = 15000
+
 export async function fetchStreams() {
   const r = await fetch('/api/v3/paths/list?itemsPerPage=200', { credentials: 'same-origin' })
   if (!r.ok) throw new Error(`api ${r.status}`)
   const data = await r.json()
-  return (data.items || [])
-    .filter(p => p.ready && (p.tracks || []).length > 0)
-    .map(p => {
-      const [user, ...rest] = p.name.split('/')
-      return {
-        id: p.name,                                  // e.g. techy/VanguardTraining
-        user,
-        title: rest.join('/') || p.name,
-        viewers: (p.readers || []).length,
-        since: p.readyTime,
-        tracks: p.tracks || [],
-      }
+  const ready = (data.items || []).filter(p => p.ready && (p.tracks || []).length > 0)
+  const byName = new Map(ready.map(p => [p.name, p]))
+  const now = Date.now()
+  for (const p of ready) if (!firstSeen.has(p.name)) firstSeen.set(p.name, now)
+  for (const k of [...firstSeen.keys()]) if (!byName.has(k)) firstSeen.delete(k)
+  const out = []
+  for (const p of ready) {
+    if (p.name.endsWith('.webrtc')) continue       // audio mirror: played through its source's panel, never its own
+    const tracks = p.tracks || []
+    const audio = tracks.filter(t => !VIDEO.has(t))
+    const needsMirror = audio.length > 0 && !audio.includes('Opus')   // AAC etc. cannot cross WebRTC
+    const mirror = byName.get(p.name + '.webrtc')
+    if (needsMirror && !mirror && now - firstSeen.get(p.name) < MIRROR_WAIT_MS) continue   // give the mirror a moment to come up
+    const [user, ...rest] = p.name.split('/')
+    out.push({
+      id: p.name,                                  // e.g. techy/VanguardTraining
+      user,
+      title: rest.join('/') || p.name,
+      whep: mirror ? mirror.name : p.name,         // WebRTC plays the Opus mirror when there is one; HLS always the source
+      viewers: (p.readers || []).length + (mirror ? (mirror.readers || []).length - 1 : 0),   // the mirror's ffmpeg is one reader
+      since: p.readyTime,
+      tracks,
     })
-    .sort((a, b) => (a.since || '').localeCompare(b.since || ''))
+  }
+  return out.sort((a, b) => (a.since || '').localeCompare(b.since || ''))
 }
 
 export const whepUrl = id => `/webrtc/${id}/whep`