[FFmpeg-devel] [PATCH] lavc/vp9: fix reference frame dimensions check

[Linjie Fu]

With the description in frame size with refs semantics (SPEC 7.2.5),
it is a requirement of bitstream conformance that for at least one
reference frame has the valid dimensions.

Modify the check to make sure the decoder works well in the condition
that not all references frames have valid dimensions.

Signed-off-by: Linjie Fu <linjie.fu at intel.com>
---
Fix the the decoding faiure for frames with dimension-ilegal refs.
Verifying with native vp9 and libvpx-vp9 decoder, the md5 result matches.
https://github.com/webmproject/libvpx/blob/master/vp9/decoder/vp9_decodeframe.c#L1580

 libavcodec/vp9.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/libavcodec/vp9.c b/libavcodec/vp9.c
index 7aaae9b..61d60ef 100644
--- a/libavcodec/vp9.c
+++ b/libavcodec/vp9.c
@@ -794,6 +794,7 @@ static int decode_frame_header(AVCodecContext *avctx,
 
     /* check reference frames */
     if (!s->s.h.keyframe && !s->s.h.intraonly) {
+        int valid_ref_frame = 0;
         for (i = 0; i < 3; i++) {
             AVFrame *ref = s->s.refs[s->s.h.refidx[i]].f;
             int refw = ref->width, refh = ref->height;
@@ -807,18 +808,23 @@ static int decode_frame_header(AVCodecContext *avctx,
             } else if (refw == w && refh == h) {
                 s->mvscale[i][0] = s->mvscale[i][1] = 0;
             } else {
+                /* Check to make sure at least one of frames that */
+                /* this frame references has valid dimensions. */
                 if (w * 2 < refw || h * 2 < refh || w > 16 * refw || h > 16 * refh) {
-                    av_log(avctx, AV_LOG_ERROR,
+                    av_log(avctx, AV_LOG_WARNING,
                            "Invalid ref frame dimensions %dx%d for frame size %dx%d\n",
                            refw, refh, w, h);
-                    return AVERROR_INVALIDDATA;
+                    continue;
                 }
                 s->mvscale[i][0] = (refw << 14) / w;
                 s->mvscale[i][1] = (refh << 14) / h;
                 s->mvstep[i][0] = 16 * s->mvscale[i][0] >> 14;
                 s->mvstep[i][1] = 16 * s->mvscale[i][1] >> 14;
             }
+            valid_ref_frame++;
         }
+        if (!valid_ref_frame)
+            return AVERROR_INVALIDDATA;
     }
 
     if (s->s.h.keyframe || s->s.h.errorres || (s->s.h.intraonly && s->s.h.resetctx == 3)) {
-- 
2.7.4