[FFmpeg-devel] [PATCH] h264 deblocking result doesn't match with SIMD on and off.

[Michael Niedermayer]

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.

could you provide a h264 file that decodes differently?

all reference streams that we claim to support decode binary identical
as far as i remember

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

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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