libavcodec/vc1dec.c:883: error: Uninitialized Value
  The value read from n_slices1 was never initialized.

libavcodec/vc1dec.c:883:32: 
881.                 s->end_mb_y = (i == n_slices     ) ? mb_height : FFMIN(mb_height, slices[i].mby_start % mb_height);
882.             else
883.                 s->end_mb_y = (i <= n_slices1 + 1) ? mb_height : FFMIN(mb_height, slices[i].mby_start % mb_height);
                                    ^
884. 
885.             if (s->end_mb_y <= s->start_mb_y) {
