libavcodec/vc1dec.c:919: error: Uninitialized Value
  The value read from mv_f[_] was never initialized.

libavcodec/vc1dec.c:919:13: 
917.     } else {
918.         int dominant = 0;
919.         if (mv_f[0] + mv_f[1] + mv_f[2] + mv_f[3] > 2)
                 ^
920.             dominant = 1;
921.         valid_count = get_chroma_mv(mvx, mvy, mv_f, dominant, &tx, &ty);
