Examples fail to compile with incompatible-pointer-types errors
OggzReadPacket() is of the type int (*)(void *, oggz_packet *, long int, void *)
Functions read_packet() have signature int (*)(void *, ogg_packet *, long int, void *)
Despite embedding ogg_packet, oggz_packet is of a different type, and modern C refuses to silently cast between them.
And all op->whatever should be replaced with op->op.whatever in said read_packet() functions.
See also: https://bugs.gentoo.org/929253