MediaStream IDs with webrtcbin

[Florian Echtler]

Thanks, Matt - I've tried to call get-transceivers and that gives me 3 
transceiver objects as expected (2 video, 1 audio), but the mid property of all 
of them is always empty (None in Python).

I'm currently calling get-transceivers after on-negotiation-created, but that 
seems to be the wrong point in time?

Also, I initially tried to register for on-new-transceiver, but that never seems 
to get called at all...

What am I missing here?

Thanks and best, Florian

On 07/09/2021 05:28, Matthew Waters wrote:
> 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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