[FFmpeg-devel] [HACK] 50% faster H.264 decoding

Ronald S. Bultje rsbultje
Tue Aug 17 00:48:41 CEST 2010


On Mon, Aug 16, 2010 at 6:40 PM, Jason Garrett-Glaser
<darkshikari at gmail.com> wrote:
> On Mon, Aug 16, 2010 at 3:35 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
>> On Wed, Aug 11, 2010 at 5:32 PM, Jason Garrett-Glaser
>> <darkshikari at gmail.com> wrote:
>>> 13. Use MPEG-2 MC for chroma MC, since we know that MVs are
>>> fullpel-only. ?Simplify edge emulation stuff accordingly too.
>> Does h264 chroma subpel actually use a memcpy shortcut if it's
>> fullpel? I don't remember exactly, but I don't think it has such a
>> shortcut for chroma, only for luma.
> It doesn't. ?It should at least have a shortcut for the 0,0 motion
> vector because its very high probability (relative to other fullpel
> motion vectors that result in no chroma interpolation). ?For other
> cases, it might or might not be worthwhile to add a branch in the asm
> to the 1D-only case.
> See ffvp8 for an example of zero-MV shortcutting (done in the C code, not asm).

Right, that's what I was thinking. In fact, I think I could also add
one for mx&7==0-only or my&7==0-only handling, I would expect that to
still be significantly faster than the one where both are non-fullpel.


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