Non-ID3 tag data about an MP3 track is stored by i Tunes itself and therefore doesn't travel with the MP3 file.You can view most of this non-ID3 Tag data by examining the "i Tunes Music Library.xml" file.To cut to the chase, this is the format of ID3 Tag v1.0: So there's 125 bytes of data and that's the order it must appear in.A player will know that the first 30 bytes is the Song title text (or "string"), the next 30 is the Artist string, etcetera.Originally ID3 tags held just this basic text-only information about a music file.They were a standard size and held standardized information.
Don't forget: name, artist, album, and comment are all elements of track.
Currently there are five versions of ID3 tags: v1.0 and v1.1, and v2.2, v2.3, and v2.4.
Each successive version attempts to improve on the storage capabilities of the previous version while maintaining backward compatibility.
Since these frames can be placed in any order it is up to the player to make sense of the tag data (again, if you are really really really interested... The upshot of all this is that ID3 v2.x tags can contain Unicode text strings of up to 256 characters.
That means your Title, Artist, Album, and Comment fields can be really long if your MP3s use ID3 tag v2.x.