I have the feeling that the bug is there: https://searchfox.org/mozilla-central/source/dom/media/mediasource/TrackBuffersManager.cpp#1215-1220 We check if the audio configuration hasn't changed and ignore the init segment if so. The problem is that the AudioInfo == operator doesn't check if that trackID has changed.
Bug 1679283 Comment 4 Edit History
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I have the feeling that the bug is there: https://searchfox.org/mozilla-central/source/dom/media/mediasource/TrackBuffersManager.cpp#1215-1220 We check if the audio configuration hasn't changed and ignore the init segment if so. maybe the trackID isn't properly populated on the AudioInfo; IIRC the demuxer only ever parse the first track with MSE and always assume the trackID is 0.