[FFmpeg-devel] [PATCH] h264 deblocking result doesn'tmatch with SIMD on and off.

[Michael Niedermayer]

On Sat, May 23, 2009 at 08:56:49PM -0400, Jason Garrett-Glaser wrote:
> On Sat, May 23, 2009 at 8:35 PM, Haruhiko Yamagata <h.yamagata at nifty.com> wrote:
> >> On Sun, May 24, 2009 at 12:40:18AM +0900, Haruhiko Yamagata wrote:
> >>>
> >>> In h264 decoder, deblocking result doesn't match with SIMD on and off.
> >>>
> >>> In h264_loop_filter* (dsputil.c), there are several
> >>>
> >>> ? if( FFABS( p0 - q0 ) < alpha &&
> >>> ? ? ? FFABS( p1 - p0 ) < beta &&
> >>> ? ? ? FFABS( q1 - q0 ) < beta )
> >>>
> >>> In SIMD optimized functions, this is done in H264_DEBLOCK_MASK
> >>> (h264dsp_mmx.c).
> >>>
> >>> ? if (!(FFABS( p0 - q0 ) > (uint8_t)(alpha -1) ||
> >>> ? ? ? ? FFABS( p1 - p0 ) > (uint8_t)(beta ?-1) || ? // beta == 0 ? Oops :
> >>> ...
> >>> ? ? ? ? FFABS( q1 - q0 ) > (uint8_t)(beta ?-1) ))
> >>>
> >>> So the SIMD optimized functions expect alpha and beta not to be zero.
> >>> OK, let them assume it for performance.
> >>> The attached patch fixes this issue.
> >>>
> >>> The errors are usually invisible, but after a long chain of reference,
> >>> the errors accumulate and eventually get visible.
> >>>
> >>> Best regards,
> >>> Haruhiko Yamagata
> >>> ffdshow-tryouts
> >>>
> >>
> >>> ?h264.c | ? ?4 ++++
> >>> ?1 file changed, 4 insertions(+)
> >>> 089aea8ce540d5087b27de54b2a67b7b11e8d707 ?dont_deblock_if_beta_is_0.patch
> >>
> >> This patch adds the checks so they are also done for the C code
> >> this seems wastefull unless there is some advantage in it?
> >
> > If the stream has alpha ==0 or beta==0, the performance is better with the
> > patch. But it doesn't seem to be common enough.
> 
> That'll be the case in any macroblock with quantizer 15 or below.
> 
> If you're using, say, --deblock -2:-2, that would be 19 or below.
> With x264's AQ, that'll occur all the time, so I'd say keep it in even
> with C.  We have that line in x264 as well.

well then iam ok with it too

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

Those who are too smart to engage in politics are punished by being
governed by those who are dumber. -- Plato 
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