Sending out stereo: codecOptions vs codec

mediasoup libraries
1

Hi,

I’m trying to find out what the relationship is between RtpCodecCapability.channels and codecOptions.opusStereo.

In the mediasoup demo it seems the producer options just specifies opusStereo in the codecOptions: https://github.com/versatica/mediasoup-demo/blob/v3/app/lib/RoomClient.js#L803-L814 and doesn’t specify the RtpCodecCapability.

Is this sufficient or do we also need to set the codec and search for a RtpCodecCapabaility on the device that has 2 channels (and vice-versa for mono). Or how do these 2 settings interact?

2

Opus is always signalled (in the SDP) with /2 (so two channels) so hence its codecCapability.channels will be always 2, no matter you later enable stereo or not.

3

Thanks, is the same true for DTX?

And while mentioning DTX, the mediasoup demo sets dtx: true for screenshare video producers: https://github.com/versatica/mediasoup-demo/blob/v3/app/lib/RoomClient.js#L36-L39

But I don’t find this mentioned in the spec: https://w3c.github.io/webrtc-pc/#rtcrtpencodingparameters

I do find it on MDN, but there it says it’s only for audio.

So is this something new or deprecated or an error in the demo?

4

Look for “dtx” in https://mediasoup.org/documentation/v3/mediasoup/rtp-parameters-and-capabilities/

5

Yes, I saw that, but is it supported by (libwebrtc) browsers if it’s not part of the webRTC spec?

6

This is something for mediasoup (server), not for clients.

7

Ah, ok, I was confused since it was being defined on the client side in the demo. Thanks for the quick answers!

8

It’s defined in client side because it’s later propagated to the server. But you are right. In fact the dtx option in RTCRtpEncodingParameters is not even implemented in libwebrtc.