ID3 is a metadata container most often used in conjunction with the MP3 audio file format. It allows information such as the title, artist, album, track number, and other information about the file to be stored in the file itself. There are two unrelated versions of ID3: ID3v1 and ID3v2. An ID3 tag is used to embed information in an MP3 file. It is not an official specification of the MP3 format. ID3 version 1 includes simple fields such as album, artist, and title through a 30-character text field embedded at the end of the MP3 file, using 128 bytes of total data. ID3 version 2 has been totally rewritten to allow variable length fields. It includes lengthier textual information plus other information such as who encoded the file, Web sites, pictures, lyrics, and other information. The following information is from iTunes Help: