[webrtc-pc] Codec dictionary match, ignoring levels, and AV1 (#3037)

henbos has just created a new issue for https://github.com/w3c/webrtc-pc:

== Codec dictionary match, ignoring levels, and AV1 ==
Our codec match algorithm assumes media formats are the thing that needs to be "==", and highest complying bitstream levels can (sometimes) be ignored because in SDP offer/answer exchange you only need to ensure "<=" levels to ensure interoperability.

I think the mistake here is in the wording, because for AV1, all of the media format properties fall into the "<=" category:
https://aomediacodec.github.io/av1-rtp-spec/#723-usage-with-the-sdp-offeranswer-model

So "media format" and "highest complying bitstream levels", as was the words we choose to write this algorithm, are not actually two distinct categories.

Proposal:
1. Instead of saying "media format", say something like "media formats, excluding media configuration parameters that are allowed to be asymmetrical for this codec"
2. Clarify that "highest complying bitstream levels" does not only refer to "level", but any asymmetrical parameter (or whatever word we want to use here).

A clarifying NOTE would help here would help for AV1 and H.265 as prime examples

Please view or discuss this issue at https://github.com/w3c/webrtc-pc/issues/3037 using your GitHub account


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Received on Wednesday, 5 March 2025 14:36:31 UTC