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

Jason Garrett-Glaser darkshikari
Thu Jan 29 12:46:56 CET 2009

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? ;)

Dark Shikari

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