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

[christian.feldmann at gmx.de]

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:

 

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];

         }

--