How to get channel setting /2 into a recvonly webrtcbin transceiver SDP

[Matthew Waters]

Interesting, looks like a bug :)

https://tools.ietf.org/html/rfc7587#section-7 says the rtpmap 'channels'
must be 2 which GStreamer does not produce.

Could you file an issue on gitlab?

Cheers
-Matt

On 22/7/20 4:56 pm, Anthony Alba wrote:
> Problem: Cannot get SDP line (with the /2 appended)
> a=rtpmap:96 OPUS/48000/2
> from a audio recvonly transceiver on a webrtcbin
>
> I am trying to setup a recvonly webrtcbin(for audio) and taking
> guidance from here:
>
> https://stackoverflow.com/questions/57430215/how-to-use-webrtcbin-create-offer-only-receive-video
>
> When I do:
>
> direction = GstWebRTC.WebRTCRTPTransceiverDirection.RECVONLY
> caps = Gst.caps_from_string("application/x-rtp,media=opus,encoding-name=OPUS,channel-rate=48000,channels=2,payload=96")
> self.webrtc.emit('add-transceiver', direction, caps)
>
> This mostly works, and the resulting SDP looks like
> # notice channels=2 is ignored
>
> a=recvonly
> a=rtpmap:96 OPUS/48000
>
> Unfortunately my sender does not like this and wants
> a=rtpmap:96 OPUS/48000/2
>
> When I read back the transceiver, the codec_preferences member looks correct:
>
> Transceiver: application/x-rtp, media=(string)audio,
> encoding-name=(string)OPUS, clock-rate=(int)48000, channels=(int)2,
> payload=(int)96;
>
> What is the correct way to get the channel setting /2 append to the SDP offer?
>
> Mangling the SDP in the application before sending to the peer works,
> but I was hoping for a more canonical way to do this. The full
> pipeline is eventually
>
> # after pad-added signal
> webrtcbin ! decodebin ! queue !  audioconvert ! audioresample ! autoaudiosink
>
> Alternatively, what is the correct way to tell webrtcbin to add a
> transceiver that will emit the desired SDP?
>
>
> Thanks
> Anthony Alba
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> gstreamer-devel at lists.freedesktop.org
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