iTunes and ID3 tags
11 Mar 2005I have a Sony MP-40 car radio that reads CDs with MP3 files. However, since I started using iTunes to create my MP3 CDs, I sometimes seem to lose the ID3 tags (Title/ Artist/ Album). I now know why: iTunes writes ID3v2 tags, and the Sony only handles ID3v1 (MP40 PDF).
Main differences:
- ID3v1 tags are written in a 128 byte fixed-length field at the end of the audio file.
Song title 30 characters Artist 30 characters Album 30 characters Year 4 characters Comment 30 characters Genre 1 byte
- ID2v2 can accommodate variable length tags, and allows storing them at the beginning and/or the end of the file.
+-----------------------------+ | Header (10 bytes) | +-----------------------------+ | Extended Header | | (variable length, OPTIONAL) | +-----------------------------+ | Frames (variable length) | +-----------------------------+ | Padding | | (variable length, OPTIONAL) | +-----------------------------+ | Footer (10 bytes, OPTIONAL) | +-----------------------------+
There are advantages for both systems:
- prepending the ID3 info (add it in the beginning of the file) is essential for non-random access (e.g. streaming) and low bandwidth situations. You want to display the information as fast as possible, before the music starts playing.
- appending the ID3 data (add it at the end of the file) makes it easier to edit. If you have a 50MB music podcast, and you change the Album/Artist info (which is necessary in a lot of cases, the authors don’t always pay attention to good tagging – thank god Doppler can do this automatically), in a lot of cases the whole file has to be rewritten, and this takes several seconds.
iTunes actually does the most sensible thing: it prepends ID3v2 tags and uses the ‘padding’ to reserve about 1,6 KB of space. So if new ID3 info has to be added, it can take some of the place reserved by the padding and iTunes only needs to change the first 1,6KB of the file, and leave the rest untouched. This combines the advantages of appending and prepending.
The default location of an ID3v2 tag is prepended to the audio so that players can benefit from the information when the data is streamed. It is however possible to append the tag, or make a prepend/append combination.
(from id3.org)
Until I change my car stereo, my only option is to change the ID3 format of my files before I burn them to a MP3 CD. iTunes can do this (the ‘Advanced’/’Convert ID3 tags’ option), but it’s still a drag.
