[rtcweb] Is support for two-byte RTP header extensions mandatory?
Philipp Hancke <philipp.hancke@googlemail.com> Fri, 22 September 2023 07:42 UTC
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From: Philipp Hancke <philipp.hancke@googlemail.com>
Date: Fri, 22 Sep 2023 09:42:30 +0200
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Subject: [rtcweb] Is support for two-byte RTP header extensions mandatory?
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This spawned from a discussion with Harald Alvestand. Neither https://www.rfc-editor.org/rfc/rfc5285.html nor its successor https://www.rfc-editor.org/rfc/rfc8285 nor the RTP usage draft https://datatracker.ietf.org/doc/html/rfc8834#name-header-extensions provide guidance on whether WebRTC mandates two byte header extensions and how/if this is negotiated using offer-answer. Nor is this negotiated as extmap-allow-mixed only implies support (if you can mix one-byte and two-byte versions you must support both) Another issue here is how an implementation that does not support two-byte extensions should deal with an extension id 15 which is forbidden in the one-byte variant. Should offerers skip this id when generating offers? Firefox rejects ids greater than or equal to 15 https://github.com/web-platform-tests/wpt/pull/41843 complaining libWebRTC does not support two-byte extensions (which it does). libWebRTC-based browsers implement and can negotiate up to 16 extensions these days (with some not enabled by default yet) This is not a practical problem yet since some of those extensions are not very useful when used together which means most real-world scenarios need less than 15 extensions. The path forward seems to agree that two-byte extensions are a thing and cross fingers that implementations will continue to need less than 15 extensions for long enough to get Firefox fixed. Thoughts? Philipp
- [rtcweb] Is support for two-byte RTP header exten… Philipp Hancke