[FFmpeg-cvslog] vp9: fix mvref finding to adhere to bug in libvpx.

[Ronald S. Bultje]

ffmpeg | branch: master | Ronald S. Bultje <rsbultje at gmail.com> | Sat Nov  9 10:52:49 2013 -0500| [dd3d0f46bdb0b9bd204159c67f522cd6f3db7e7c] | committer: Clément Bœsch

vp9: fix mvref finding to adhere to bug in libvpx.

Fixes a particular youtube video that I unfortunately can't share.

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=dd3d0f46bdb0b9bd204159c67f522cd6f3db7e7c
---

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

diff --git a/libavcodec/vp9.c b/libavcodec/vp9.c
index 3539a54..d26f122 100644
--- a/libavcodec/vp9.c
+++ b/libavcodec/vp9.c
@@ -984,7 +984,10 @@ static void find_ref_mvs(VP9Context *s,
             if (mv->ref[0] != ref && mv->ref[0] >= 0) {
                 RETURN_SCALE_MV(mv->mv[0], s->signbias[mv->ref[0]] != s->signbias[ref]);
             }
-            if (mv->ref[1] != ref && mv->ref[1] >= 0) {
+            if (mv->ref[1] != ref && mv->ref[1] >= 0 &&
+                // BUG - libvpx has this condition regardless of whether
+                // we used the first ref MV and pre-scaling
+                AV_RN32A(&mv->mv[0]) != AV_RN32A(&mv->mv[1])) {
                 RETURN_SCALE_MV(mv->mv[1], s->signbias[mv->ref[1]] != s->signbias[ref]);
             }
         }
@@ -997,7 +1000,10 @@ static void find_ref_mvs(VP9Context *s,
         if (mv->ref[0] != ref && mv->ref[0] >= 0) {
             RETURN_SCALE_MV(mv->mv[0], s->signbias[mv->ref[0]] != s->signbias[ref]);
         }
-        if (mv->ref[1] != ref && mv->ref[1] >= 0) {
+        if (mv->ref[1] != ref && mv->ref[1] >= 0 &&
+            // BUG - libvpx has this condition regardless of whether
+            // we used the first ref MV and pre-scaling
+            AV_RN32A(&mv->mv[0]) != AV_RN32A(&mv->mv[1])) {
             RETURN_SCALE_MV(mv->mv[1], s->signbias[mv->ref[1]] != s->signbias[ref]);
         }
     }