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Is "same PT, different FMTP lines" allowed in BUNDLE? #2766
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I think the following fiddle is forbidden https://www.rfc-editor.org/rfc/rfc8843#name-payload-type-pt-value-reuse says |
Sounds pretty disallowed, filed https://crbug.com/webrtc/14420 |
Just want to add, in that same thread alvestrand@ says "the way RTP works, there can't be two different codec configurations for the same payload type on the same transport in the same direction", and I trust his knowledge of RTP semantics. I just know how Chrome/libwebrtc works, and the fact that it supports different FMTP lines doesn't mean that's correct. |
seems we have a bug in multiple browsers, Firefox accepts the fiddle as well. |
Current status: we can't fix browsers since there is too much actual usage and we don't know who needs to fix their code. |
While working on w3c/webrtc-stats#662 (comment), we discovered that Chrome is able to handle a BUNDLEd transport where different m= sections use the same codec and payload type but where the FMTP line is different. See fiddle (you'd think this would throw, but it doesn't).
The idea that it should be possible to have different FMTP lines for the same PT and transport was expressed by @jan-ivar here and @taylor-b here, while @fippo strongly believes that this should be illegal and there is a bug in Chrome.
I don't know what BUNDLE says but different FMTP lines sounds wrong to me. What should be the correct behavior? (If it is not, some recent code to avoid duplicate RTCCodecStats objects in libwebrtc could be simplified.)
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