[FFmpeg-cvslog] avcodec/mpeg4videodec: Fix GMC with videos of dimension 1

[Michael Niedermayer]

ffmpeg | branch: release/2.8 | Michael Niedermayer <michael at niedermayer.cc> | Sat Jun 24 13:45:35 2017 +0200| [7ee48d9de118a26e51ef1e2b8b570022ace46145] | committer: Michael Niedermayer

avcodec/mpeg4videodec: Fix GMC with videos of dimension 1

Fixes: runtime error: shift exponent -1 is negative
Fixes: 2338/clusterfuzz-testcase-minimized-5153426541379584

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 4976a3411f71518d17a57e373b62517f066648fd)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=7ee48d9de118a26e51ef1e2b8b570022ace46145
---

 libavcodec/mpeg4videodec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
index 9e85dfac74..060bed5817 100644
--- a/libavcodec/mpeg4videodec.c
+++ b/libavcodec/mpeg4videodec.c
@@ -170,7 +170,7 @@ static int mpeg4_decode_sprite_trajectory(Mpeg4DecContext *ctx, GetBitContext *g
     int a     = 2 << s->sprite_warping_accuracy;
     int rho   = 3  - s->sprite_warping_accuracy;
     int r     = 16 / a;
-    int alpha = 0;
+    int alpha = 1;
     int beta  = 0;
     int w     = s->width;
     int h     = s->height;