[FFmpeg-devel] Bug in VMAF calculation for 10 bit comparison

[Paul B Mahol]

On 9/14/22, christian.feldmann at gmx.de <christian.feldmann at gmx.de> wrote:
> Hi,
>
> I was debugging some VMAF calculation in ffmpeg when I stumbled on this bug
> in the latest master commit (9450f759748d02d1d284d2e4afd741cb0fe0c04a). Its
> in libavfilter/vf_libvmaf.c::109. The function copy_picture_data does only
> work correctly for 8 bit input. For 10 bit input, only half of the width of
> the input picture is copied. But for 10 bit inputs, 2 bytes per pixel must
> be copied. Please see this patch:
>
>

Patch is messed up, please either attach it as attachment or provide
it in some other way.

>
> libavfilter/vf_libvmaf.c | 3 ++-
>
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>
>
> diff --git a/libavfilter/vf_libvmaf.c b/libavfilter/vf_libvmaf.c
>
> index eee1c280ef..8d5ba4e2d5 100644
>
> --- a/libavfilter/vf_libvmaf.c
>
> +++ b/libavfilter/vf_libvmaf.c
>
> @@ -108,6 +108,7 @@ static enum VmafPixelFormat pix_fmt_map(enum
> AVPixelFormat av_pix_fmt)
>
>  static int copy_picture_data(AVFrame *src, VmafPicture *dst, unsigned bpc)
>
> {
>
> +    const int bytes_per_value = bpc > 8 ? 2 : 1;
>
>      int err = vmaf_picture_alloc(dst, pix_fmt_map(src->format), bpc,
>
>                                   src->width, src->height);
>
>      if (err)
>
> @@ -117,7 +118,7 @@ static int copy_picture_data(AVFrame *src, VmafPicture
> *dst, unsigned bpc)
>
>          uint8_t *src_data = src->data[i];
>
>          uint8_t *dst_data = dst->data[i];
>
>          for (unsigned j = 0; j < dst->h[i]; j++) {
>
> -            memcpy(dst_data, src_data, sizeof(*dst_data) * dst->w[i]);
>
> +            memcpy(dst_data, src_data, bytes_per_value * dst->w[i]);
>
>              src_data += src->linesize[i];
>
>              dst_data += dst->stride[i];
>
>          }
>
> --
>
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