VideoRoom track's owner identification

Participant identification

Jitsi just like Membrane support multiple peers on a single shared peer connection.

There is a problem of identifying each peer based on the incoming tracks. The SFU needs to keep track of its participants (things like display name ect.) and pass that information to the client when needed.

How Jitsi does that?

The low-level code that is responsible for identifying incoming tracks with participants is available here:

https://github.com/jitsi/lib-jitsi-meet/blob/baa78aca40541b87b44d5218bcdef2a7be5fee59/modules/RTC/TraceablePeerConnection.js#L813

Jitsi listens on remote tracks being added. Then it does manual search on the remoteDescription.sdp string to obtain necessary information.

First it checks the transceiver for mid field, if not found then if falls back to searching for msid that equals to the current stream id. (It all depends on what plan the browser is using but as far as I know Unifed Plan is now a standard). Then the sdp is filtered for lines that include mid or msid fields that has been found in previous step. In resulting lines we filter out received lines to get corresponding ssrc.

The main goal here is to obtain corresponding ssrc of incoming track. Then a request is sent to the server with given ssrc to return track’s participant id. And further down the line if participant is not in client’s cache, again a request is sent to obtain participant’s information.

How should we do that?

What fields can we use to query information about given participant? Each participant will see the same mid values, from what I recall msid will differ for each participant same goes with ssrc and when querying the server it will have to identify the caller to get the proper mapping of outgoing streams (with mid it can do a really quick check).

And how should we get participants information, after getting a new track by sending query request or the server itself should first send information about incoming participant?

[mat-hek]

Couldn’t we just send the mapping of (mid/msid/whatever) => user_data along with SDP? This case is a bit different than screensharing, at least if we assume that the user data changes only when SDP changes.

[mickel8]

Maybe. It’s worth mentioning that besides ssrc there is also cname which stands for canonical name and is probably more valuable id than ssrc.