[FFmpeg-cvslog] avcodec/mpegvideo_motion: Use a field from the current frame if the last is unavailable in DMV & 16x8

[Michael Niedermayer]

ffmpeg | branch: release/1.2 | Michael Niedermayer <michaelni at gmx.at> | Fri Apr 19 14:46:31 2013 +0200| [d1da1c8384c625f2ecb0040c60702ebb5523a0d1] | committer: Michael Niedermayer

avcodec/mpegvideo_motion: Use a field from the current frame if the last is unavailable in DMV & 16x8

Fixes null pointer dereference

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
(cherry picked from commit 42bcc4082d644342171216fcf597cde75421a4d7)

Signed-off-by: Michael Niedermayer <michaelni at gmx.at>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=d1da1c8384c625f2ecb0040c60702ebb5523a0d1
---

 libavcodec/mpegvideo_motion.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libavcodec/mpegvideo_motion.c b/libavcodec/mpegvideo_motion.c
index f443b8e..6fddab7 100644
--- a/libavcodec/mpegvideo_motion.c
+++ b/libavcodec/mpegvideo_motion.c
@@ -827,8 +827,8 @@ static av_always_inline void MPV_motion_internal(MpegEncContext *s,
         for(i=0; i<2; i++){
             uint8_t ** ref2picture;
 
-            if(s->picture_structure == s->field_select[dir][i] + 1
-               || s->pict_type == AV_PICTURE_TYPE_B || s->first_field){
+            if((s->picture_structure == s->field_select[dir][i] + 1
+               || s->pict_type == AV_PICTURE_TYPE_B || s->first_field) && ref_picture[0]){
                 ref2picture= ref_picture;
             }else{
                 ref2picture = s->current_picture_ptr->f.data;
@@ -857,6 +857,9 @@ static av_always_inline void MPV_motion_internal(MpegEncContext *s,
                 pix_op = s->dsp.avg_pixels_tab;
             }
         }else{
+            if (!ref_picture[0]) {
+                ref_picture = s->current_picture_ptr->f.data;
+            }
             for(i=0; i<2; i++){
                 mpeg_motion(s, dest_y, dest_cb, dest_cr,
                             s->picture_structure != i+1,