ID3v1

ID3v1 is a metadata container that is appended to the end of an MP3 audio file. It was the first widely adopted standard for storing information about an MP3 track, such as the title, artist, album, year, and genre. The ID3v1 tag occupies the last 128 bytes of an MP3 file. This fixed size made it simple to implement and widely compatible, as it did not interfere with the audio data itself.

The ID3v1 tag structure consists of several fields. The first three bytes are a header, typically "TAG". Following this is a 30-byte field for the song title, a 30-byte field for the artist, a 30-byte field for the album, a 4-byte field for the year, an 1-byte field for the comment, and finally a 1-byte field for the track number (which is sometimes used as part of the comment field in some variations). The last byte is a byte for the genre, which uses a predefined list of 149 possible values.

Due to its limitations, such as the fixed and small size of its fields and a restricted genre list, ID3v1 was eventually superseded by ID3v2. ID3v2 tags offer more flexibility, can be placed at the beginning or end of a file, and support a much wider range of metadata, including lyrics, cover art, and more detailed information. However, ID3v1 remains compatible with many older MP3 players and software that may not fully support or recognize ID3v2 tags.