avcodec/libaomdec: Set SAR based on RenderWidth and RenderHeight

This is the same thing we do in libdav1d.c

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

libavcodec/libaomdec.c

@@ -197,6 +197,14 @@ static int aom_decode(AVCodecContext *avctx, void *data, int *got_frame,
         }
         if ((ret = ff_get_buffer(avctx, picture, 0)) < 0)
             return ret;
+
+        av_reduce(&picture->sample_aspect_ratio.num,
+                  &picture->sample_aspect_ratio.den,
+                  picture->height * img->r_w,
+                  picture->width * img->r_h,
+                  INT_MAX);
+        ff_set_sar(avctx, picture->sample_aspect_ratio);
+
         if ((img->fmt & AOM_IMG_FMT_HIGHBITDEPTH) && img->bit_depth == 8)
             image_copy_16_to_8(picture, img);
         else