[FFmpeg-devel] [PATCH] avcodec/ffv1dec_template: Optimize common case in run mode

[Michael Niedermayer]

On Thu, May 23, 2019 at 10:57:14AM +0200, Carl Eugen Hoyos wrote:
> Am Do., 23. Mai 2019 um 01:47 Uhr schrieb Michael Niedermayer
> <michael at niedermayer.cc>:
> >
> > Fixes: Timeout (14sec -> 9sec)
> > Fixes: 13398/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFV1_fuzzer-5664106709778432
> >
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  libavcodec/ffv1dec_template.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/libavcodec/ffv1dec_template.c b/libavcodec/ffv1dec_template.c
> > index 1b7f6c4bf5..0b1d176ba1 100644
> > --- a/libavcodec/ffv1dec_template.c
> > +++ b/libavcodec/ffv1dec_template.c
> > @@ -86,11 +86,19 @@ static av_always_inline int RENAME(decode_line)(FFV1Context *s, int w,
> >                          run_mode = 2;
> >                      }
> >                  }
> > +                if (sample[1][x - 1] == sample[0][x - 1]) {
> > +                    while (run_count > 1 && w-x > 1) {
> > +                        sample[1][x] = sample[0][x];
> > +                        x++;
> > +                        run_count--;
> > +                    }
> > +                } else {
> 
> Does this change have a measurable effect on your usual sample files?

decode_line() becomes 1% faster for fate/vsynth2-ffv1.avi
for another fate sample there is a 0.5% speedup
the effect should be bigger for files with "flat" colored areas
the new faster branch is used in 97-100% of the cases in fate samples
compared to the older more complex (which i tested)

vsynth3-ffv1-v3-bgr0.avi had the lowest percentual useage of about 97%


[...]
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