[Ffmpeg-devel] [PATCH] snow cached halfpel

Michael Niedermayer michaelni
Mon Mar 13 11:35:25 CET 2006


On Sun, Mar 12, 2006 at 11:02:48PM -0800, Loren Merritt wrote:
> Note: I this patch is not ready for inclusion, I am just posting it as-is 
> for anyone who cares.
> Stores halfpel interpolated frames, so that each call to hpel mc is just a 
> copy, and each qpel mc is just a pavgb. This makes encoding with obme+qpel 
> 9% faster, and obme+hpel 6% faster. But due to the extra branch in 
> pred_block, decoding is 1% slower.

well, iam sure the decoding speedloss can be avoided somehow ...

> I expect that even better encoding speed gains can be had using the same 
> method in mpeg4+qpel and snow+epzs, but that will involve much more 
> invasive changes.

this trick doesnt work with mpeg4+qpel, at least not without a quality loss
the reason is that mpeg4 mirrors the 8tap qpel filter at the block borders
so that instead of having to fetch a 15x15 block for each 8x8 block only a
9x9 block needs to be fetched ...

IIRC xvid supports or did support at some point in the past such cached 
halfpel interpolated frames, so maybe one of the xvid devels could comment 
on the speed/quality of it?



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