Re: [FFmpeg-devel] [PATCH v4] avcodec/h264_mb: Fix tmp buffer overlap

[Bin Peng <pengbin@visionular.com>]

Hi, Michael,

Should I add the attached bitstream to the FATE test?

https://trac.ffmpeg.org/attachment/ticket/11357/inter_weighted_bipred2.264

Regards
Bin Peng


On 2024/12/24 15:49, Bin Peng wrote:
> When decoding a bitstream with weighted-bipred enabled,
> the results on ARM and x86 platforms may differ.
> 
> The reason for the inconsistency is that the value of
> STRIDE_ALIGN differs between platforms. And STRIDE_ALIGN
> is set to the buffer stride of temporary buffers for U
> and V components in mc_part_weighted.
> 
> If the buffer stride is 32 or 64 (as on x86 platforms),
> the U and V pixels can be interleaved row by row without
> overlapping, resulting in correct output.
> However, on ARM platforms where the stride is 16,
> the V component will overwrite part of the U component's pixels,
> leading to incorrect predicted pixels.
> 
> Fixes: ticket 11357
> 
> Signed-off-by: Bin Peng <pengbin@visionular.com>
> ---
>  libavcodec/utils.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
> index 2dbd677920..d280e1c324 100644
> --- a/libavcodec/utils.c
> +++ b/libavcodec/utils.c
> @@ -147,6 +147,7 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
>      int i;
>      int w_align = 1;
>      int h_align = 1;
> +    int stride_align = STRIDE_ALIGN;
>      AVPixFmtDescriptor const *desc = av_pix_fmt_desc_get(s->pix_fmt);
>  
>      if (desc) {
> @@ -342,13 +343,14 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
>          // increasing witdth ensure that the temporary area is large enough,
>          // the next rounded up width is 32
>          *width = FFMAX(*width, 32);
> +        stride_align = FFMAX(stride_align, 32);
>      }
>      if (s->codec_id == AV_CODEC_ID_SVQ3) {
>          *width = FFMAX(*width, 32);
>      }
>  
>      for (i = 0; i < 4; i++)
> -        linesize_align[i] = STRIDE_ALIGN;
> +        linesize_align[i] = stride_align;
>  }
>  
>  void avcodec_align_dimensions(AVCodecContext *s, int *width, int *height)

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