Tell SDP negotiation to negotiate support for non-standard codecs

[alvestrand]

As part of support for encrypted media, the RTP packetizer and depacketizer of senders and receivers have to be able to:

a) know that it's pointless to try to look inside the packet for codec-dependent data
b) know what rules to apply when packetizing and depacketizing the frames

The architecturally cleanest solution would be to ask the SDP negotiation machinery to negotiate a PT value to use with the encrypted and packetized frames, and have the ability to retrieve the resulting PT value so that when enqueueing a frame, the processor can set a payload type that elicits the expected behavior.

[fippo]

see also w3c/webrtc-extensions#100 - even though I think your scope is intentionally more limited

[alvestrand]

A proposal is in the slide deck for March

[dontcallmedom-bot]

This issue was discussed in the minutes of WebRTC March 2023 meeting – 21 March 2023 (WebRTC Encoded Transform: Negotiating Custom Codecs)

[dontcallmedom-bot]

This issue was discussed in WebRTC June 2023 meeting – 27 June 2023 (Encoded Transform Codec Negotiation)