[FFmpeg-devel] [PATCH v2] avcodec/apedec: fix prediction

["zhilizhao(赵志立)"]

> On Jun 30, 2022, at 5:09 PM, Zhao Zhili <quinkblack at foxmail.com> wrote:
> 
> From: Zhao Zhili <zhilizhao at tencent.com>
> 
> Regression since ed0001482a74b60f3d5bc5.
> 
> Tested with:
> ./ffmpeg -i foo.ape -f md5 -
> for samples in #9816 and #2239.
> 
> It gives the same result as before ed0001482a for ticket #9816,
> and doesn't break ticket #2239.

OK, It did break #8918. The compression_level is different between #9816
and #8918, I have no idea if it can be used as the condition, or just
some random bug in the encoders which created those files.

> 
> Signed-off-by: Zhao Zhili <zhilizhao at tencent.com>
> ---
> libavcodec/apedec.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/apedec.c b/libavcodec/apedec.c
> index a7c38bce1b..f5c0f75f7f 100644
> --- a/libavcodec/apedec.c
> +++ b/libavcodec/apedec.c
> @@ -1198,7 +1198,7 @@ static av_always_inline int predictor_update_filter(APEPredictor64 *p,
>                   p->buf[delayB - 3] * p->coeffsB[filter][3] +
>                   p->buf[delayB - 4] * p->coeffsB[filter][4];
> 
> -    p->lastA[filter] = decoded + ((int64_t)((uint64_t)predictionA + (predictionB >> 1)) >> 10);
> +    p->lastA[filter] = decoded + ((int32_t)((uint32_t)predictionA + ((int32_t)predictionB >> 1)) >> 10);
>     p->filterA[filter] = p->lastA[filter] + ((int64_t)(p->filterA[filter] * 31ULL) >> 5);
> 
>     sign = APESIGN(decoded);
> -- 
> 2.35.3
> 
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