ID3 tag

A set of meta-data in an MP3, WMA, AAC or Ogg Vorbis audio file that describes its contents, including song title, artist, album, year, comment, CD track and genre. ID3 tags are used for searching as well as displaying the title being played. In many cases, the ID3 tags are not filled in or are erroneous, and an ID3 "tagger" utility can be used to edit them.

ID3 Format
The 128-byte ID3 tag resides at the end of the file and comprises 30-byte text fields, a 4-byte year and a 1-byte genre, which contains a predefined category code from 0 to 79. In Version 1.1 (ID3v1.1), the original CD track number was added at the end of the comment field. Version 2 (ID3v2) is much more elaborate with a variable number of frames that can hold a total of 1MB. For more information, visit www.id3.org.

Why Not on the Original CDs?
Many believe the lack of meta-data on the original audio CD to be an extreme lack of vision. As engineers were developing it in the late 1970s, it would have been simple to reserve a few thousand bytes out of the 650 million to store this obviously useful data. See online music database.