WebRTC: Renegotiation in firefox

Question

According to this article, re-negotiation is implemented in firefox v38 and we can add remove streams from same peerconnections without creating new ones, but I am unable to find any working demos to support that claim, and when I tried it, two users chating in video mode, I changing one of their stream to audio, I get the error:

NotSupportedError: removeStream not yet implemented

this tells the same, but this tells renegotiation events are supported, but isn't removeStream key part of renegotiation? I am using firefox version 39 in windows 7. I am confused, renegotiation is not yet supported in firefox, right?

Answer 1

Renegotiation is supported in Firefox.

Firefox just never implemented removeStream because the spec had changed to addTrack and removeTrack by the time renegotiation was implemented (some are suggesting that its removal was too hasty, so it may come back). addStream still works for backwards compatibility, because Firefox already supported it.

Note that removeTrack confusingly takes the RTCRtpSender returned from addTrack so the API is not a drop-in.

A polyfill would look something like this:

mozRTCPeerConnection.prototype.removeStream = function(stream) {
  this.getSenders().forEach(sender =>
      stream.getTracks().includes(sender.track) && this.removeTrack(sender));
}

The move to tracks was done to give users more flexibility, since tracks may belong to multiple streams, and not all tracks in a stream need be sent over a PeerConnection (or the same PeerConnection).

See this answer to a different question for a renegotiation example that works in Firefox.