this version of tremor requires a nil check on close_func
https://svn.xiph.org/trunk/Tremor/vorbisfile.c
/* Generated by ffconf */
#ifndef AVUTIL_AVCONFIG_H
#define AVUTIL_AVCONFIG_H
#define AV_HAVE_BIGENDIAN 0
#define AV_HAVE_FAST_UNALIGNED 1
#endif /* AVUTIL_AVCONFIG_H */