[MPlayer-users] Re: divx 6

[Loren Merritt]

On Sat, 29 Apr 2006, Rich Felker wrote:

> On Fri, Apr 28, 2006 at 11:57:13AM -0700, Loren Merritt wrote:
>> On Fri, 28 Apr 2006, Rich Felker wrote:
>>> gmc is intentionally not supported because it's an idiotic feature. It
>>> makes streams that are MUCH slower to decode and does not improve
>>> quality measurably.
>>
>> MUCH = 5%? because that's how much gmc costs after I mmx'ed it.
>> That said, I agree on gmc not doing much of anything, so 5% is way too
>> expensive for a nop.
>
> Cache thrashing is not any fixed percentage. Full GMC means you have
> to use an extra buffer, unless you have some crazy optimization to
> avoid that. And that can have all kinds of cache impacts which depend
> on resolution, audio codec, other processes running, filters in use,
> etc. etc. etc.

I didn't use a buffer in my implementation of gmc. There wasn't one the C 
version either.
gmc is a bilinear interpolation of the same reference frame that normal 
MC uses, evaluated in 16x16 blocks like everything. The only difference 
is that gmc needs 16bit math, and the interpolation coefficients change 
between pixels.

--Loren Merritt