Re: [payload] WGLC for draft-ietf-payload-vp8-03 ending March 1st
Stephan Wenger <stewe@stewe.org> Wed, 21 March 2012 17:27 UTC
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From: Stephan Wenger <stewe@stewe.org>
To: Patrik Westin <pwestin@google.com>, "payload@ietf.org" <payload@ietf.org>, "ron.even.tlv@gmail.com" <ron.even.tlv@gmail.com>, "abegen@cisco.com" <abegen@cisco.com>
Thread-Topic: [payload] WGLC for draft-ietf-payload-vp8-03 ending March 1st
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Date: Wed, 21 Mar 2012 17:27:28 +0000
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Subject: Re: [payload] WGLC for draft-ietf-payload-vp8-03 ending March 1st
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Hi Patrick, On 3.21.2012 16:46 , "Patrik Westin" <pwestin@google.com> wrote: >Answers to questions regarding draft-ietf-payload-vp8-03. > >Answers to question from Stephan Wenger > >The decoder does not exhibit a significant non-uniformity >computational complexity, we assume that the call set up process will >provide a method for negotiating the max received resolution. Given >that this is a commonly needed feature, we do not define any >codec-specific way of doing this negotiation here. We will add a note >about the need for it. Sorry, but I do not think this is sufficient. A simple note will not do, as it, in practice, renders the VP8 payload close to unusable and insecure in heterogenous environments, for reasons I mentioned in my previous email. A normative reference to a resolution negotiation document would help somewhat, but AFAIK, there is no document in the IETF space that you could reference today. If there were one, please normatively reference it. Beyond the payload format: I'm not quite sure whether a generic (SDP-) code point for resolution negotiation, independent from other properties, would be such a great idea. For example, think in MPEG terms, profiles and levels. Profiles select coding tools based on (among other things) complexity and application requirements. Levels are selected in units roughly representing to picture size and frame rate, something like macroblocks per second. What one should shoot for, if one were trying to create a single-dimension resolution negotiation draft, would be the rough equivalent of signaling a level, not just a spatial resolution. And even with that, while in VP8 the complexity should be roughly proportional to the MB/sec measure, this is not true for other codecs that have a developed profile system. If one were creating a generic solution for resolution signaling, profile specific complexity behavior (which, quite obviously, is highly codec dependent) would have to be taken care of. Also, please take a look at the HEVC-type parallelization tools. (A very preliminary description of the problem with parallelization tools can be found in http://tools.ietf.org/html/draft-schierl-payload-rtp-h265-00, section 1.) Briefly put, with HEVC, you can sometimes decode a bitstream even if a single core or CPU could not bear the load--if your bitstream is tailored to support parallel decoding and if you have multiple cores. It's an HEVC specific thing, so it has to live in the HEVC payload. But how would this be compatible with a hypothetical generic resolution negotiation mechanism? To summarize, I think you should consider the inclusion of code points allowing to negotiate decoding complexity (macroblocks per second, decoding memory requirements (maximum picture size), and perhaps also maximum framerate. Stephan > > >Answers to questions from Roni Even > >1. Good idea, we will add it to figure 2. > >2. We will reformulate the paragraph so that it is clear that it's >only summarizing information from RFC 6386. > >3. The packet does not belong to a discardable frame, will add a note >about it. > >4. Will change to reference RFC 4566 > > > >-Patrik Westin >
- [payload] WGLC for draft-ietf-payload-vp8-03 endi… Ali C. Begen (abegen)
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Stephan Wenger
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Roni Even
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Ali C. Begen (abegen)
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Roni even
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Ali C. Begen (abegen)
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Ali C. Begen (abegen)
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Patrik Westin
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Stephan Wenger
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Harald Alvestrand
- [payload] WGLC for draft-ietf-payload-vp8-03 endi… tom harper
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Patrik Westin
- Re: [payload] WGLC for draft-ietf-payload-vp8-03 … Ali C. Begen (abegen)