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Re: [rtcweb] Followup to discussion of O/A and codecs from Friday session

Roman Shpount <roman@telurix.com> Fri, 08 April 2016 22:27 UTC

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Date: Fri, 08 Apr 2016 18:27:30 -0400
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From: Roman Shpount <roman@telurix.com>
To: Taylor Brandstetter <deadbeef@google.com>
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Subject: Re: [rtcweb] Followup to discussion of O/A and codecs from Friday session
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On Fri, Apr 8, 2016 at 6:18 PM, Taylor Brandstetter <deadbeef@google.com>
wrote:

> In Section 6 of RFC 3264:
>
>> The answerer MUST send using a media format in the offer that is also listed in the answer
>>
>> So, if X offers A and B, and Y answers B, how would Y be able to send A?
> It's not in both the offer and the answer.
>
>
A does not have to be in both offer and answer. Offer/Answer is declarative
capability exchange with each side declaring what it is willing to receive.
It is not intended to pick a single codec. Negotiation is considered
successful if there is at least one common codec, but there are no other
requirements. Each party can send any codec remote party is willing to
receive and can switch between the codecs remote party supports at any
time. So in this example, Y can not only send A but can switch between A
and B at any time.

Also, answer can include codecs which were not present in the offer, so the
whole situation can be reversed.
_____________
Roman Shpount

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