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ID3 Tag Overview
What is ID3?
ID3 tag is a small chunk of extra data in the end of the file one could get the MP3 file to carry information about the audio and not just the audio itself. It is used because the audio format MPEG layer I, layer II and layer III (MP3) has no native way of saving information about the contents, except for some simple yes/no parameters like "private", "copyrighted" and "original home" (meaning this is the original file and not a copy). A solution to this problem was introduced with the program "Studio3" by Eric Kemp alias NamkraD in 1996.

The placement of the tag, as the data was called, was probably chosen as there were little chance that it should disturb decoders. In order to make it easy to detect a fixed size of 128 bytes was chosen. The tag was placed in the end of an MP3 file and has the following layout :

  • Song title - 30 characters
  • Artist - 30 characters
  • Album - 30 characters
  • Year - 4 characters
  • Comment - 30 characters
  • Genre - 1 byte

Three extra bytes can be found at the very beginning of the tag, before the song title. These three bytes are always "TAG" and is the identification that this is indeed an ID3 tag.

The byte value you enter in the genre field corresponds to a value in a predefined list. The list that Eric Kemp created had 80 entries, ranging from 0 to 79.

What is ID3v2?
ID3v2 is a new tagging system that lets you put enriching and relevant information about your audio files within them. In more down to earth terms, ID3v2 is a chunk of data prepended to the binary audio data. Each ID3v2 tag holds one or more smaller chunks of information, called frames. These frames can contain any kind of information and data you could think of such as title, album, performer, website, lyrics, equalizer presets, pictures etc.

One of the design goals were that the ID3v2 should be very flexible and expandable. It is very easy to add new functions to the ID3v2 tag, because, just like in HTML, all parsers will ignore any information they don't recognize. Since each frame can be 16 MB and the entire tag can be 256 MB you'll probably never again be in the same situation as when you tried to write a useful comment in the old ID3 being limited to 30 characters.

Speaking of characters, the ID3v2 supports Unicode so even if you use the Bopomofo character set you'll be able to write in your native language. You can also include in which language you're writing in so that one file might contain e.g. the same lyrics but in different languages.

Even though the tag supports a lot of byte consuming capabilities like inline pictures and even the possibility to include any other file, ID3v2 still tries to use the bytes as efficient as possibly. If you convert an ID3v1 tag to an ID3v2 tag it is even likely that the new tag will be smaller. If you convert an ID3v1 tag where all fields are full (that is, all 30 characters are used in every field) to an ID3v2 tag it will be 56 bytes bigger. This is the worst case scenario for ID3v1 to ID3v2 conversion.

Since it's so easy to implement new functionality into ID3v2, one can hope that we'll see a lot of creative uses for ID3v2 in the future. E.g. there is a built-in system for rating the music and counting how often you listen to a file, just to mention some brainstorm results that are included. This feature can be used to build playlists that play your favourite songs more often than others.

Some main features of ID3v2 tag

  • Has several new text fields such as composer, conductor, media type, BPM, copyright message, etc. and the possibility to design your own as you see fit.
  • The tag supports Unicode.
  • The ID3v2 tag is a container format, just like IFF or PNG files, allowing new frames (chunks) as evolution proceeds.
  • Is able to contain volume, balance, equalizer and reverb settings.
  • Is able to contain images and just about any file you want to include.
  • Residing in the beginning of the audio file makes it suitable for streaming.
  • Has an "unsynchronization scheme" to prevent ID3v2-incompatible players to attempt to play the tag.
  • Maximum tag size is 256 megabytes and maximum frame size is 16 megabytes.
  • Byte conservative and with the capability to compress data it keeps the files small.
  • Isn't entirely focused on musical audio, but also other types of audio.
  • Can contain lyrics as well as music-synced lyrics (karaoke) in almost any language.
  • Could be linked to CD-databases such as CDDB.
  • Supports enciphered information, linked information and weblinks.
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