libavcodec/vp56.c:621: error: Uninitialized Value
  The value read from alpha_offset was never initialized.

libavcodec/vp56.c:621:13: 
619.             FFSWAP(AVFrame *, s->framep[VP56_FRAME_GOLDEN],
620.                               s->framep[VP56_FRAME_GOLDEN2]);
621.             buf += alpha_offset;
                 ^
622.             buf_size -= alpha_offset;
623.         }
