skiped mbs in interlaced b frames fix

Originally committed as revision 2946 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpeg12.c

@@ -499,8 +499,9 @@ void mpeg1_encode_mb(MpegEncContext *s,
             cbp |= 1 << (5 - i);
     }
     
-    if (cbp == 0 && !first_mb && (mb_x != s->mb_width - 1 || (mb_y != s->mb_height - 1 && s->codec_id == CODEC_ID_MPEG1VIDEO)) && 
-        ((s->pict_type == P_TYPE && s->mv_type == MV_TYPE_16X16 && (motion_x | motion_y) == 0) ||
+    if (cbp == 0 && !first_mb && s->mv_type == MV_TYPE_16X16 &&
+        (mb_x != s->mb_width - 1 || (mb_y != s->mb_height - 1 && s->codec_id == CODEC_ID_MPEG1VIDEO)) && 
+        ((s->pict_type == P_TYPE && (motion_x | motion_y) == 0) ||
         (s->pict_type == B_TYPE && s->mv_dir == s->last_mv_dir && (((s->mv_dir & MV_DIR_FORWARD) ? ((s->mv[0][0][0] - s->last_mv[0][0][0])|(s->mv[0][0][1] - s->last_mv[0][0][1])) : 0) |
         ((s->mv_dir & MV_DIR_BACKWARD) ? ((s->mv[1][0][0] - s->last_mv[1][0][0])|(s->mv[1][0][1] - s->last_mv[1][0][1])) : 0)) == 0))) {
         s->mb_skip_run++;