[iOS] Muting local mic causes brief volume drop in other participants' audio (stopTrackOnMute tears down AVAudioSession)

[jmw1493]

SDK version: stream_video 1.3.1

Platform: iOS only

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Description

When a speaker mutes or unmutes their microphone in an audio room, the playback volume of other active speakers briefly drops for ~1-2 seconds before recovering.

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Root Cause

When the audio track is first published, _createAndPublishTrack calls publishAudioTrack without passing stopTrackOnMute, so it uses the parameter default of true, which gets baked into the track object:

_createAndPublishTrack()
  → publishAudioTrack(track: it.data)
  // publishAudioTrack has: bool stopTrackOnMute = true  ← origin of true
    → audioTrack.copyWith(stopTrackOnMute: true)  // stored on the track object

Then when muting:

call.setMicrophoneEnabled(enabled: false)
  → rtcManager.setMicrophoneEnabled(enabled: false)
    → _setTrackEnabled(trackType: audio, enabled: false)
      → _toggleTrackMuteState(track, muted: true)
        → muteTrack(trackId: track.trackId)  // no stopTrackOnMute override passed
          → originalTrack.copyWith(stopTrackOnMute: null)  // null = no change, keeps true
          → track.stopTrackOnMute == true
          → track.stop()  // ← releases hardware mic, deactivates AVAudioSession

track.stop() fully releases the hardware microphone and deactivates AVAudioSession. Since iOS uses a single shared audio session for both mic input and speaker output, this interruption briefly cuts the playback of all incoming remote audio streams.

The same issue occurs on unmute — unmuteTrack calls track.recreate() when stopTrackOnMute == true, which reinitializes the entire WebRTC audio pipeline, causing a second AVAudioSession disruption.

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Expected Behavior

Muting the local mic should call track.disable() only (sets mediaTrack.enabled = false at the WebRTC layer — stops sending audio without touching AVAudioSession). Remote audio playback should be completely unaffected.

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Suggested Fix

In _toggleTrackMuteState (lib/src/webrtc/rtc_manager.dart), pass stopTrackOnMute: false for audio tracks, or expose it as a parameter on setMicrophoneEnabled:

Future<RtcLocalTrack> _toggleTrackMuteState({
  required RtcLocalTrack track,
  required bool muted,
}) async {
  if (muted) {
    await muteTrack(
      trackId: track.trackId,
      stopTrackOnMute: track.trackType == SfuTrackType.audio ? false : null,
    );

Note: muteTrack already accepts stopTrackOnMute as an optional override param in 1.3.1 — the plumbing exists, it just isn't wired up from the public API path.

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Reproduction Steps

1. Join an audio room as a speaker with 1+ other active speakers
2. Confirm you can hear other participants clearly
3. Tap mute
4. Observe ~1-2 second dip in other participants' volume

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Workaround

None available from user code. call.muteSelf() hits the same code path via a server round-trip and also requires muteUsers permission.