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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 22:21 UTC

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References: <5708256F.5080205@alum.mit.edu> <57082A21.7010005@alvestrand.no>
Date: Fri, 08 Apr 2016 18:21:23 -0400
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From: Roman Shpount <roman@telurix.com>
To: Harald Alvestrand <harald@alvestrand.no>
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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 6:01 PM, Harald Alvestrand <harald@alvestrand.no>
wrote:

> This indicates that the answer's omission of a codec does not allow the
> offerer to deallocate resources that it has reserved for decoding that
> type of stream (such as hardware).
>
> Under this interpretation, if I reserve hardware for decoding VP8 and
> H.264, and I get back an answer that indicates VP8 only, I cannot
> deallocate my H.264 resources, since the answerer may choose to send me
> H.264 anyway.
>
>
Based on what I heard from multiple people (including Jonathan Rosenberg
when this document was originally discussed), Offer/Answer was always
intended to be asymmetrical. Each side can declare all the codecs it is
willing to receive and can send any codec remote party supports. I saw
multiple examples of this being implemented and used in exactly this manner.

In your example, if you need to free resources for H.264, you need to do
another Offer/Answer exchange in which you will send an offer with VP8 only.

Regards,
_____________
Roman Shpount

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