Pullback should be performed on scaled motion vectors in B-frames

Originally committed as revision 8750 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/vc1.c

@@ -2304,6 +2304,12 @@ static inline void vc1_pred_b_mv(VC1Context *v, int dmv_x[2], int dmv_y[2], int
     s->mv[0][0][1] = scale_mv(s->next_picture.motion_val[1][xy][1], v->bfraction, 0, s->quarter_sample);
     s->mv[1][0][0] = scale_mv(s->next_picture.motion_val[1][xy][0], v->bfraction, 1, s->quarter_sample);
     s->mv[1][0][1] = scale_mv(s->next_picture.motion_val[1][xy][1], v->bfraction, 1, s->quarter_sample);
+
+    /* Pullback predicted motion vectors as specified in 8.4.5.4 */
+    s->mv[0][0][0] = av_clip(s->mv[0][0][0], -60 - (s->mb_x << 6), (s->mb_width  << 6) - 4 - (s->mb_x << 6));
+    s->mv[0][0][1] = av_clip(s->mv[0][0][1], -60 - (s->mb_y << 6), (s->mb_height << 6) - 4 - (s->mb_y << 6));
+    s->mv[1][0][0] = av_clip(s->mv[1][0][0], -60 - (s->mb_x << 6), (s->mb_width  << 6) - 4 - (s->mb_x << 6));
+    s->mv[1][0][1] = av_clip(s->mv[1][0][1], -60 - (s->mb_y << 6), (s->mb_height << 6) - 4 - (s->mb_y << 6));
     if(direct) {
         s->current_picture.motion_val[0][xy][0] = s->mv[0][0][0];
         s->current_picture.motion_val[0][xy][1] = s->mv[0][0][1];