libavcodec/vp56.c:503: error: Uninitialized Value
  The value read from alpha_offset was never initialized.

libavcodec/vp56.c:503:5: 
501.     AVFrame *const p = s->framep[VP56_FRAME_CURRENT];
502.     int remaining_buf_size = buf_size;
503.     int is_alpha, av_uninit(alpha_offset);
         ^
504. 
505.     if (s->has_alpha) {
