[Ffmpeg-devel] [PATCH] fix mpeg4 lowres chroma bug and increase h264/mpeg4 MC speed

Michael Niedermayer michaelni
Mon Feb 12 12:49:30 CET 2007


Hi

On Mon, Feb 12, 2007 at 02:24:58AM -0800, Trent Piepho wrote:
> On Mon, 12 Feb 2007, Michael Niedermayer wrote:
> > On Sun, Feb 11, 2007 at 03:40:39PM -0800, Trent Piepho wrote:
> > > On Fri, 9 Feb 2007, Michael Niedermayer wrote:
> > > > > Do you disagree with me that avg_h264_chroma_mc4_mmx2 is completely broken?
> > >
> > > How come you never answer this?
> >
> > well, its brokenness depends upon what it is supposed to do, i didnt write
> > that code ....
> >
> > we could add a requirement that some extra bytes must be allocated after the
> > buffer but that might cause problems for some users of ffmpeg and wont help
> > with the multithreading also it doesnt seem like the correct solution for this
> > rather minor internal issue
> >
> > maybe using the plain C version of the code for the rightmost column would be
> > an option ...
> 
> I'm not talking about *PUT*_h264_chroma_mc4_mmx2, but *AVG*_h264_chroma_mmx2.
> That function does not overwrite the destination bytes, but averages them
> with the result.  The first two bytes are averaged correctly, the second
> two bytes are averaged with zero.  Adding extra padding or using the C
> version on the rightmost column won't fix it at all.  The entire image is
> incorrect.  It is supposed to compute result = (new + old)/2, but what it
> is doing is result = (new + old/2)/2

oops, you are correct, avg_h264_chroma_mmx2 is broken


> 
> > > Why do you discard some times in your TIMER code?  Is the goal just to
> > > discard those times in which an interrupt occured?
> >
> > yes
> 
> That's not what's is doing, there are far too many skips for that to
> be the case.

indeed ill try to improve START/STOP_TIMER

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Everything should be made as simple as possible, but not simpler.
-- Albert Einstein
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