libavcodec/error_resilience.c:685: error: Uninitialized Value
  The value read from prev_y was never initialized.

libavcodec/error_resilience.c:685:53: 
683. 
684. 
685.                     if (s->mv[0][0][0] != prev_x || s->mv[0][0][1] != prev_y) {
                                                         ^
686.                         fixed[mb_xy] = MV_CHANGED;
687.                         changed++;
