[FFmpeg-devel] [PATCH] H.264: Faster DC handling (idct_dc and more)

Michael Niedermayer michaelni
Thu Jan 29 20:54:09 CET 2009

On Thu, Jan 29, 2009 at 03:46:56AM -0800, Jason Garrett-Glaser wrote:
> On Mon, Jan 26, 2009 at 5:32 PM, Jason Garrett-Glaser
> <darkshikari at gmail.com> wrote:
> > The first of these patches modifies ffmpeg to implement x264-style
> > scan8; this means storing nnz from luma/chroma DC in scan8.  This is
> > extremely useful because it means one can check with a single if
> > whether luma/chroma DC exists.  Normally, you can only do it in the
> > case of CABAC where the data is stored in the cbp.  This also
> > simplifies decode_residual a lot and will surely be useful for future
> > optimizations.
> >
> > The second of these patches ports an 8x8 idct_dc function from x264
> > which I just wrote (so new, in fact, it isn't in x264 yet!).  This one
> > is LGPL.  The entire patch drops chroma idct/dequant time from ~268
> > clocks to ~205 clocks on a Core 2 Conroe.  Note that there *are*
> > warnings relating to pointers in this patch--suggestions welcome on
> > the best way to clean them up without making the source messy.
> >
> > And yes, I tested adding the ifs I used in the DC-only section to the
> > other chroma decoding section--it makes it slower, probably because
> > you almost never have chroma AC without chroma DC.
> >
> > Dark Shikari
> >
> Did this get lost in the flood of discussion about releases or something? ;)

no it got lost in my lazyness, ill look at it of course, just have many other
patches to look at as well and i tend to look at easy ones first
(h264 is never easy :)


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates
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