libavcodec/vc1dec.c:5600: error: Uninitialized Value
  The value read from n_slices1 was never initialized.

libavcodec/vc1dec.c:5600:32: 
5598.                 s->end_mb_y = (i == n_slices     ) ? mb_height : FFMIN(mb_height, slices[i].mby_start % mb_height);
5599.             else
5600.                 s->end_mb_y = (i == n_slices1 + 1) ? mb_height : FFMIN(mb_height, slices[i].mby_start % mb_height);
                                     ^
5601.             vc1_decode_blocks(v);
5602.             if (i != n_slices)
