RTC Peer Connection - receiving a stream twice

I have an instance RTCPeerConnection

with ontrack

:

 newConnection.ontrack = receivedStream // remote

      

        
        
        
      

    

Once the SDP exchange is complete and the peer adds its local stream:

 connection.addStream(stream); // local

      

        
        
        
      

    

I can see that it receivedStream

gets called twice for each thread. - Checking e.track

shows me that the first call is for the track audio

and the second is for the track video

.

What's weird is that checking e.streams[0]

and calling getTracks

on this gives me two MediaStreamTracks

- one for audio and another for video:

So, I connect four MediaStreamTracks

to two calls receivedStream

despite calling addStream

once.

receivedStream

is here:

 function receivedStream(e) {
        var stream = e.streams[0]; // this gets invoked twice when adding one stream!
        if (!stream) {
            throw new Error("no stream found");
        };
        // this gets me the corresponding connection
        waitForStream(stream.id).then(function (connection) {
            // get element
            targetVideoElement[0].srcObject = stream; // this now gets called twice per stream - once for audio, once for video
        }).catch(function (error) {
           // log
        });
    }