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

[Jason Garrett-Glaser]

On Mon, Aug 16, 2010 at 3:35 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
> Hi,
>
> 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).

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