Hands On: Tagging your music

The shift towards digital music has brought us many benefits.

Compressed music files mean we can fit hundreds of albums on our media players. However, one often overlooked advantage is that cataloguing music libraries is now much easier.

All music players, such as Windows Media Player 11 and Apple’s iTunes, allow you to browse albums by artists, album name or song title and you can create playlists comprising a variety of music styles and artists without having to shuffle CDs or cassettes.

What’s more, intelligent playlist creation technology, such as the Genius feature recently added to iTunes, allows you to pick a track and have a playlist automatically created for you based on its style and genre.

What makes all of this possible is some clever additional data called tags that are added on to your MP3 files when they’re initially ripped from CD.

A history of id
When the MP3 format was first created it didn’t include any support for tagging. MP3 was originally designed as a way of compressing audio for transmission alongside video on broadcast systems like digital satellite and cable TV.

It wasn’t until much later that people started to use MP3 as a way of compressing and storing music. However, by the mid 1990s it became obvious it would be useful if there was a way of adding text to MP3s to describe the content of the file.

Eventually a system was developed that used a 128-byte tag at the end of the file to store artist, song and title information along with a small area for other comments. The tag went at the end of the file as a compromise to retain compatibility with existing software players.

This tagging format became know as ID3 and was soon standard. Not long after its introduction, however, it was tweaked to allow it to store track numbers, to indicate the play order of the tracks on the original source CD. This extended format became known as ID3v1.1.

However, ID3v1.1 tags weren’t without their problems. The small amount of space available for storing data meant song and album titles longer than 30 characters had to be truncated; there was a set number of predefined genres that could be used; and because the tag was added to the end of the file, it was problematic when MP3s were being streamed over a network.

It was soon obvious that a newer, more flexible tagging system was needed and by 1988 a format called ID3v2 was introduced, but despite the name it bore almost no resemblance to its predecessors.

ID3v2 was a huge leap forward in terms of design and functionality. It is much more flexible because ID3v2 tags are made up of smaller pieces of information known as frames. Not all of these frames have a set role, so almost any type of data can be stored.

It means ID3v2 tags can be used not just to add artist, album name and song title information, but also data such as album art, lyrics and web addresses. The system also includes an element of future proofing because new frame types can be added for extra functionality. Players that don’t understand new frames will ignore them so compatibility is retained.

Whereas the older tagging formats suffered from a 128-byte limit, ID3v2 tags can be up to 256MB in size, with each frame having a maximum size of 16MB. Despite the extra storage space available, the tagging system is quite frugal in its storage needs, with the creators reckoning if an ID3v1 tag is converted to an ID3v2 it will take up less space.