libavcodec/vp56.c:504: error: Uninitialized Value
  The value read from alpha_offset was never initialized.

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