MediaStream IDs with webrtcbin

[Matthew Waters]

MediaStreamId's are not really supported by webrtcbin at all currently.  
They are only there to make RTX work as required by browsers.

Also, putting ssrc's into SDP is something that's going away with the 
use of simulcast and mid/rid header extensions so I'm not entirely sure 
on the usefulness of a=ssrc msid:$val going forward in that respect.

How we usually advise to match up streams on both sides is via 'mid' 
which is both in the SDP and exposed through the transceivers on both ends.

Cheers
-Matt

On 6/9/21 5:59 pm, Florian Echtler via gstreamer-devel wrote:
> Hello everyone,
>
> there's a SO discussion on how to properly label multiple video 
> streams in a WebRTC bundle: https://stackoverflow.com/a/65412097/838719
>
> The conclusion is to add a mapping from MediaStreamIDs to "readable" 
> names, but how would I go about this with webrtcbin?
>
> AFAICT the only connection between the gstreamer pipeline and the 
> resulting SDP offer is through the payload ID:
>
> m=video 9 UDP/TLS/RTP/SAVPF 96
> [...]
> a=ssrc:647810976 msid:user3145526253 at host-b7e78eb1 webrtctransceiver0
> a=ssrc:647810976 cname:user3145526253 at host-b7e78eb1
> a=mid:video0
>
> Is there any way I can set either mid or msid from outside, or do I 
> have to parse the SDP for this to figure out how payload ID and 
> mid/msid match?
>
> Best, Florian


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