libavcodec/vc1.c:661: error: Uninitialized Value
  The value read from mvx[_] was never initialized.

libavcodec/vc1.c:661:18: 
659.             break;
660.         case 0x4:
661.             tx = mid_pred(mvx[0], mvx[1], mvx[3]);
                      ^
662.             ty = mid_pred(mvy[0], mvy[1], mvy[3]);
663.             break;
