Stereo audio playback for WebRTC on Chrome

[longnguyen2004]

I've seen that the MediaMTX server managed to get stereo audio working in Chrome in WebRTC, maybe you guys can have a look and see how it's done?

[Rokamun]

This is already supported assuming you're sending stereo Opus.
https://mistserver.org/demos/whipwhep.html

Broadcast through that and you get stereo opus by default. Or use a VoD without bframes and stereo opus and you'd get stereo sound as well.

[longnguyen2004]

Unfortunately my source is from OBS. Anyway, stereo audio playback is only working for Firefox, Chrome is downmixing the audio to mono on playback.

I've read up a bit about the problem and it seems like Chrome needs some extra parameters to be present in the SDP to allow stereo playback, namely stereo=1 and sprop-stereo=1. See https://issues.webrtc.org/issues/41481053 for more detail.

[Rokamun]

That is something we should be able to add.

[Rokamun]

Adding this here as an update. We've tried adding these to the SDP, however it didn't seem to have much effect as it would still come out as mono sound. So I would say this is probably not enough (or we added it wrong). 🤔

At least chrome is claiming it is stereo, but if you play sound from just left or just right it comes through both. So it's converted to double mono.

https://github.com/DDVTECH/mistserver/tree/testing/opusstereo
7ea428b

Maybe it has success on your side, or maybe we just misunderstood how the SDP should've looked like.

[longnguyen2004]

I think you also need to inject it to the local description on the client side, add stereo=1;sprop-stereo=1 here