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Re: [rtcweb] JSEP: codecs in answer: MUST vs. MAY

Iñaki Baz Castillo <ibc@aliax.net> Tue, 24 October 2017 21:15 UTC

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From: Iñaki Baz Castillo <ibc@aliax.net>
Date: Tue, 24 Oct 2017 23:15:11 +0200
Message-ID: <CALiegf=J1xKcLif81Lmk85p6YW9soJLsvDS_wyi1kPzxkXbqOA@mail.gmail.com>
To: Jonathan Lennox <jonathan@vidyo.com>
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Subject: Re: [rtcweb] JSEP: codecs in answer: MUST vs. MAY
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I thought that one of the reasons for adopting SDP in WebRTC was that
it allows rapid implementation.
Are we still defining how codecs are negotiated? Is not even that
properly defined in the SDP O/A spec?

On 24 October 2017 at 21:58, Jonathan Lennox <jonathan@vidyo.com> wrote:
> JSEP (section 5.3.1) seems to be inconsistent about how whether
> locally-supported codecs that weren’t listed in a remote offer MUST, or MAY,
> be included in an answer:
>
>    o  If codec preferences have been set for the associated transceiver,
>       media formats MUST be generated in the corresponding order,
>       regardless of what was offered, and MUST exclude any codecs not
>       present in the codec preferences.
>
>    o  Otherwise, the media formats on the m= line MUST be generated in
>       the same order as those offered in the current remote description,
>       excluding any currently unsupported formats.  Any currently
>       available media formats that are not present in the current remote
>       description MUST be added after all existing formats.
>
>    o  In either case, the media formats in the answer MUST include at
>       least one format that is present in the offer, but MAY include
>       formats that are locally supported but not present in the offer,
>       as mentioned in [RFC3264], Section 6.1.  If no common format
>       exists, the m= section is rejected as described above.
>
>
> The first two paragraphs certainly seem to indicate that these codecs MUST
> be included in the answer; however, the third paragraph suddenly weakens
> this to a MAY.
>
> Is the intent of the third paragraph simply to restate RFC 3264’s loose
> requirements, whereas the first two are JSEP’s more binding ones?  If so, I
> think this should be stated more clearly, otherwise the required behavior is
> unclear.
>
> _______________________________________________
> rtcweb mailing list
> rtcweb@ietf.org
> https://www.ietf.org/mailman/listinfo/rtcweb
>



-- 
Iñaki Baz Castillo
<ibc@aliax.net>

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