A pointer to the OggVorbis_File structure--this is used for ALL the externally visible vorbisfile
functions. Once this has been called, the same OggVorbis_File
struct should be passed to all the vorbisfile functions.
Return Values
0 for success
less than zero for failure:
OV_EREAD - A read from media returned an error.
OV_ENOTVORBIS - Bitstream is not Vorbis data.
OV_EVERSION - Vorbis version mismatch.
OV_EBADHEADER - Invalid Vorbis bitstream header.
OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.