ID3 Space

Attached to the beginning or end of an MP3 file is the ID3 information. Items within the ID3 tag can include artist and title, copyright information, terms of use, proof of ownership, an encapsulated thumbnail image, and comments. There are actually two variants of the ID3 specification: ID3v1 and ID3v2, and while the potential differences between them are great, virtually all modern MP3 players handle files with tags in either format. ID3v2 tags are not only capable of storing a lot more information than ID3v1 tags, they appear at the beginning of the bitstream, rather than at the end. The reason for this is simple; when an MP3 file is being broadcast or streamed rather than simply downloaded, the player needs to be able to display all of this information throughout the duration of the track, not at the end when it's too late.

It is unfortunate that ID3 tags ever ended up being tagged onto the end of MP3 files to begin with. It would have been much better if all MP3 files stored their ID3 data at the beginning rather than at the end of the file. As it stands, some MP3 players will simply give up if actual audio data is not encountered within the first few frames. While players developed to the actual ISO MPEG specification know how to handle either type, the specification itself is unfortunately vague on this point. It simply states that a player should look for a "sync header," without specifying exactly where the seeking should start and stop. This laxness in the spec has caused some controversy among developers of ID3-enabled applications, who naturally don't want their applications seeking blindly through 1GB image files, should the user happen to hand one to the application. Fortunately, the ID3v2 spec is more specific on the matter.

More information regarding ID3 tags can be found on its home page: http://www.id3.org/. This site includes a brief history of ID3 tags and an explanation of how they further function in relation to audio files.