[PATCH] Fix crash of decoder on MPEG2 interlaced streams (issue 2367)

[anatoly]

---
 libavcodec/mpeg12.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/libavcodec/mpeg12.c b/libavcodec/mpeg12.c
index 3c73627..45c1881 100644
--- a/libavcodec/mpeg12.c
+++ b/libavcodec/mpeg12.c
@@ -1640,6 +1640,8 @@ static int mpeg_decode_slice(Mpeg1Context *s1, int mb_y,
     AVCodecContext *avctx= s->avctx;
     const int field_pic= s->picture_structure != PICT_FRAME;
     const int lowres= s->avctx->lowres;
+    const int check_mb_inter = field_pic && !s->first_field &&
+        s->pict_type == FF_P_TYPE && !s->last_picture.data[0];
 
     s->resync_mb_x=
     s->resync_mb_y= -1;
@@ -1763,7 +1765,12 @@ static int mpeg_decode_slice(Mpeg1Context *s1, int mb_y,
         s->dest[1] +=(16 >> lowres) >> s->chroma_x_shift;
         s->dest[2] +=(16 >> lowres) >> s->chroma_x_shift;
 
+        if (!check_mb_inter || s->mb_intra ||
+            s->picture_structure != s->field_select[0][0] + 1) {
         MPV_decode_mb(s, s->block);
+        } else {
+            av_log(avctx, AV_LOG_ERROR, "Some restrictions for inter prediction are broken, skipping macroblock\n");
+        }
 
         if (++s->mb_x >= s->mb_width) {
             const int mb_size= 16>>s->avctx->lowres;
-- 
1.7.1


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