We need to support urn:ietf:params:rtp-hdrext:sdes:mid as specified in https://tools.ietf.org/html/draft-ietf-mmusic-sdp-bundle-negotiation-12#section-13 This will require signaling work to emit/receive the SDP attributes, and pass them on to the media code, as well as updating MediaPipelineFilter to work with this extension instead of the old unified-plan stream-correlator.

This also depends on support for this extension in the webrtc.org code, which is not yet present.

Most recent spec link https://tools.ietf.org/html/draft-ietf-mmusic-sdp-bundle-negotiation-36#section-14 I think this is needed to be able to do simulcast PERC with the unified plan. Unfortunately it looks like even the 49 webrtc.org landing does not offer any support for this yet (not surprising since Chrome still has no support for unified).

Mass change P3->P4 to align with new Mozilla triage process.

Note: there is code in JsepSessionImpl.cpp which should get updated once this is resolved https://searchfox.org/mozilla-central/rev/0b613c3887789f7786cd3131dfe9648398f4a6ac/media/webrtc/signaling/src/jsep/JsepSessionImpl.cpp#1017