These are links to technical-Ressources from other projects, which help to understand certain things.

ID3

• structure of id3v2.4
• frames contained in id3v2
• id3v2.4 details on the frames
• set of libraries for id3v2

MusicBrainz

• MusicBrainz Client-Library HOWTO

freedb

• freedb file-format
• DISCID Howto
• cddb/freedb protocol

Ogg Vorbis

• Ogg Vorbis comment field specification
• Ogg logical and physical bitstream overview