[Firefox] Modify audio while playback takes too long (around 5 seconds)

[testeur-990]

Environment

• The MPD passes the DASH-IF Conformance Tool on https://conformance.dashif.org/
• The stream has correct Access-Control-Allow-Origin headers (CORS)
• There are no network errors such as 404s in the browser console when trying to play the stream
• The issue observed is not mentioned on https://github.com/Dash-Industry-Forum/dash.js/wiki/FAQ
• The issue occurs in the latest reference client on http://reference.dashif.org/dash.js/ and not just on my page

Link to playable MPD file: the issue can be reproduced easyly with your test stream :
https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/manifest.mpd
Dash.js version: 4.7.4 master
Browser name/version: Firefox

Steps to reproduce

1-Open http://reference.dashif.org/dash.js/latest/samples/dash-if-reference-player/index.html on firefox
2- Play https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/manifest.mpd
3- Change audio track

Observed behavior

The audio takes around 5 seconds to change, and this issue only happens on Firefox

Console output

[2684015][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-fr-audio-fr-mp4a.mp4 , Range:6178730-6276225 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2684240][Stream] Stream -  Process track changed at current time 316.665395 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2684889][AbrController] [audio] switching from buffer occupancy to throughput ABR rule (buffer: 0.000). [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2684889][StreamProcessor][audio] Buffer is empty! Stalling! [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685262][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:0-821 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685263][StreamProcessor][audio] [audio] lastInitializedRepresentationInfo changed to 0 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685376][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:5143445-5242488 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685436][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:5242489-5341189 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685508][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:5341190-5440026 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685508][AbrController] [audio] switching from throughput to buffer occupancy ABR rule (buffer: 12.074). [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685585][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:5440027-5539557 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685656][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:5539558-5638796 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685748][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:5638797-5737366 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685814][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:5737367-5836463 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685866][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:5836464-5935143 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685918][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:5935144-6035206 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2685981][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:6035207-6134191 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2686050][StreamProcessor][audio] OnFragmentLoadingCompleted for stream id 0 and media type audio - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/audio-en-audio-en-mp4a.mp4 , Range:6134192-6232168 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
[2686899][StreamProcessor][video] OnFragmentLoadingCompleted for stream id 0 and media type video - Url: https://media.axprod.net/TestVectors/Cmaf/clear_1080p_h264/video-H264-1080-3000k-video-avc1.mp4 , Range:134891653-137156837 [Debug.js:169:25](webpack://dashjs/src/core/Debug.js)
.............

Expected behavior

The audio should change immediately on Firefox, just like on other browsers (Chrome and Edge).
PS: I tested the same stream on the Shaka Player demo page, and the audio changed immediately.

[testeur-990]

Hello @dsilhavy ,
We were able to fix this issue by enabling the Dash.js configuration option flushBufferAtTrackSwitch. Therefore, I will close this ticket.
Thanks!