Re: [webrtc-extensions] Question: Does the current SDP setup procedure allow a stereo audio session to be initiated without munging? (#63)

Not really sure we need to specify anything new.

The opus stereo flag is using for signaling that the endpoint supports receiving stereo:

```
   stereo:  specifies whether the decoder prefers receiving stereo or
      mono signals.  Possible values are 1 and 0, where 1 specifies that
      stereo signals are preferred, and 0 specifies that only mono
      signals are preferred.  Independent of the stereo parameter, every
      receiver MUST be able to receive and decode stereo signals, but
      sending stereo signals to a receiver that signaled a preference
      for mono signals may result in higher than necessary network
      utilization and encoding complexity.  If no value is specified,
      the default is 0 (mono).
```

So the sdp mangling we currently need is a hack and all endpoints should signal `stereo=1` in the SDP.

The question is if we need an API to make the sender encode an stereo signal. 
This should be done automatically by the endpoint by checking the number of channels on the audio track to decide whether stereo or mono should be used.

In case the app wanted to use a mono source and upscale it to stereo or an stereo source and downscale to mono, I think that the best way would to do it via WebAudio before passing it to webrtc.

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Received on Thursday, 14 January 2021 15:12:16 UTC