Re: [rtcweb] VP8 / H.264 conversion without transcoding

Bossiel <bossiel@yahoo.fr> Thu, 21 November 2013 19:49 UTC

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From: Bossiel <bossiel@yahoo.fr>
Date: Thu, 21 Nov 2013 20:49:42 +0100
To: Mohammed Raad <mohammedsraad@raadtech.com>
Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] VP8 / H.264 conversion without transcoding
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Entropy decoding (CABAC/CAVLC) must be done to get the macroblock structure(partirions, motion vectors...) and residual (AC/DC coeffs). The only part you're skiping is the inverse transform, scaling and motion compensation. Also, the DPB mgt for reference pictures cannot be skiped.
This said, I don't see how this could save 1/3 CPU.

Sent from my iPhone

On Nov 21, 2013, at 20:00, Mohammed Raad <mohammedsraad@raadtech.com>; wrote:

> Hi,
> 
> Typically "smart" transcoding operates at 50 percent complexity or less. We did a fair bit of this at Dilithium Networks when I was there. There are also significant memory and delay savings when one operates on the MB level instead of the picture level. With regards to IPR, there is a significant number of current patents in this area that are not in any multi organization patent pool as far as I know. Transcoding in this way also provides quality advantages over tandem transcoding.
> 
> Obviously the more similar the codecs the more one gains. In the case of VP8 and AVC CBP, there are significant enough differences in essential elements such as the way quantization is done to make this kind of transcoding challenging, but it is possible and the numbers mentioned in the previous post sound about right.
> Mohammed
> 
> On 21 Nov 2013 20:45, "Cullen Jennings" <fluffy@iii.ca>; wrote:
>> 
>> It's a cool demo and I talked to the team that did it. This is only possible because VP8 and H.264 are very similar codecs. The idea is to not redo the motion vector computations or the DCT but just reuse the values from one format in the other since they are the same. They hope that this can provide reduce the CPU by 1/3 from a full decode then re-encode. It also help reduce loss of quality for video. Other people have talked about this idea over the years and many people think it can give a 2 to 3 speed up so that seems consistent with their goals.
>> 
>> It still requires the same bandwidth, and has similar other impacts. I can not see any way that it would not require MPEG-LA IPR for 264.
>> 
>> 
>> On Nov 21, 2013, at 6:27 AM, Mo Zanaty (mzanaty) <mzanaty@cisco.com>; wrote:
>> 
>> > This probably refers to an intelligent transcoder versus a brute force transcoder. An intelligent transcoder harvests more data during decoding than just the raw output pixels, and uses this extra data to ease encoding. Data like block partitions, motion vectors, intra modes, quantization parameters, etc.
>> >
>> > This is common for common conversions, like MPEG2 to H.264. VP8 and H.264 are much closer formats, so this can significantly improve transcoder performance.
>> >
>> > However, this is strictly a performance optimization, with no impact on IPR or licensing issues.
>> >
>> > Mo
>> >
>> >
>> > On Nov 21, 2013, at 2:51 AM, "Bossiel" <bossiel@yahoo.fr>; wrote:
>> >
>> > This could be true if they can also walk on water and change it into wine.
>> > To be serious, no it's not possible.
>> > Mamadou
>> >
>> > Sent from my iPhone
>> >
>> > On Nov 21, 2013, at 3:13, Gili <cowwoc@bbs.darktech.org>; wrote:
>> >
>> >> Hi,
>> >>
>> >> I'm at the WebRTC World conference. If I understood correctly, Zingaya just demoed what they claim is a VP8 to H.264 bridge that converts the video without transcoding. My interpretation is that they convert the surrounding packet format without re-encoding the actual video. Someone who understands codec internals (I don't) might want to validate this claim, because it could have a significant impact on the MTI debate.
>> >>
>> >> It sounds far fetched, but imagine the possibilities:
>> >>      • If the video is not being re-encoded, do H.264 royalties apply?
>> >>      • If the conversion is really cheap, is it feasible to connect a H.264 peer to a VP8 peer and have one of them convert in-line (no MCU)?
>> >> Gili
>> >> _______________________________________________
>> >> rtcweb mailing list
>> >> rtcweb@ietf.org
>> >> https://www.ietf.org/mailman/listinfo/rtcweb
>> > _______________________________________________
>> > rtcweb mailing list
>> > rtcweb@ietf.org
>> > https://www.ietf.org/mailman/listinfo/rtcweb
>> > _______________________________________________
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>> > rtcweb@ietf.org
>> > https://www.ietf.org/mailman/listinfo/rtcweb
>> 
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