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

Monty Montgomery <xiphmont@gmail.com> Thu, 21 November 2013 20:01 UTC

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Date: Thu, 21 Nov 2013 15:00:42 -0500
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From: Monty Montgomery <xiphmont@gmail.com>
To: Bossiel <bossiel@yahoo.fr>
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Subject: Re: [rtcweb] VP8 / H.264 conversion without transcoding
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On Thu, Nov 21, 2013 at 2:49 PM, Bossiel <bossiel@yahoo.fr>; wrote:
> 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.

You wouldn't even be skipping the inverse transform.  VP8 and h.264
don't use the same DCT, so you'd have to do an inverse to track
transform error propagation, which won't be the same in the two
codecs.  Unless, of course, something else rather clever is going
on...

Monty