1365797 - Ensure that unique payload types are used for bundled transports

Status: NEW

(Core :: WebRTC: Signaling, enhancement, P2)

Description

[Nils Ohlmeier [:drno]]

For bundled transports it is helpful if each payload type in a given bundled transport is unique to help serving as the last resort for demuxing incoming RTP packets.

We have code which feeds the PT as additional filter criteria to the demuxer here: http://searchfox.org/mozilla-central/source/media/webrtc/signaling/src/jsep/JsepTrack.cpp#499

If for example multiple video tracks get attached to a PeerConnection each m-section in Firefox offer will have the same PT for the same video codec, e.g. 120 for VP8 across all m-sections.
As we don't know which m-section are going to be bundled together we would have to try to offer unique PT's as much as possible across the whole offer.

In case Firefox receives an offer with non-unique PT's it again simply answers with the same non-unique PTs. We should instead try to answer with unique PT's across each bundled section.
One concern here is that this will lead to Firefox not choosing the same PT as in the offer. We hope the interoperability is not going to be too bad if we limit this feature only to bundled m-section, as bundle should hopefully only be supported by modern clients which can handle asymmetric PT's.

Comment 1

[Emma Humphries ☕️🎸🧞‍♀️✨ (she/they) [:emceeaich] (Pacific Time) use needinfo]

This is an assigned P1 bug without activity in two weeks. 

If you intend to continue working on this bug for the current release/iteration/sprint, remove the 'stale-bug' keyword.

Otherwise we'll reset the priority of the bug back to '--' on Monday, August 28th.

Comment 2

[Bulk Bug Changes for mreavy's org]

Mass change P1->P2 to align with new Mozilla triage process

Comment 3

[Nils Ohlmeier [:drno]]

I don't have the capacity any more to work on this any time soon.