ID3v1 and ID3v2 tags, what's the difference?

Now maybe you wonder, what's the difference between them all, and why do those darn computer people always have to mess things up with different versions of everything?


Allow me to explain:

It all started several years ago, when the mp3-format was all new and not nearly as widespread as today. At this time, most files on PC-computers had the short 8.3 name format, so it was practically impossible to infer what artist and title an mp3 had by only reading its filename. A couple of guys became quite annoyed with this and put together a little program that would store this data inside the mp3-files themselves. As a quick fix they simply appended all the data as a 128 byte static datastructure at the end of the mp3 files. Although this limited the tag field sizes to 30 characters each or below, for most artist name and titles this was sufficient. The whole thing worked quite fine for them and after a while it became implemented in an mp3-player, and then in another mp3-player, and before they knew it their little quick fix had become a world-wide standard for saving info in mp3:s.

There were two things about these tags (ID3v1.0) that annoyed people. First, they had no storage space for tracknumbers. This was because at the time that this tag was created there were practically no full mp3 albums in circulation, only single files (this in turn mostly due to the fact that 50-100 Mb was quite a lot of data back then, when 1.44 Mb floppy disks were the standard means of data transportation), so track numbers weren't really that important. Second, when you add up all the artist names and song names in the world, there are actually quite a few that exceed the 30 character limit.

The first problem, with the track numbers, was solved by someone by "stealing" 2 bytes from the end of the comment-field, which was the least used field of the ID3v1.0 tags, and using it to store a binary tracknumber value instead. This became known as the ID3v1.1 standard, but most programs did not support it (e.g. Winamp). Luckily, due to the standard implementation of text string storage in computers (null-terminated strings) it could be done in such a way that these new tags were fully backward-compatible with the ID3v1.0 tags, so even if a program didn't support v1.1 tags, they were still fully readable and the tracknumber data was simply ignored if present.

The second problem on the other hand could not be solved nearly as easy. After all, the v1-tags had started out as a 10-minute hack that mistakenly turned into a world-wide standard, and it was time to rethink the whole thing from the start and come up with a new design that was worthy the number of users around the world that were actually using it every day. So, this was exacly what a couple of guys did, and the results were the ID3v2 format.

The ID3v2 tag is fundamentally different from ID3v1 tags. Some important differences are:

• ID3v1 tags have a limit to how big each field can be. This is not the case in ID3v2 tags.
  
  
• ID3v1 tags have a fixed set of possible fields (artist, title, album, comment, year, genre, and in the case of ID3v1.1 tags, track number). This is not the case for ID3v2 tags. They have a fully dynamical structure, not only allowing arbitrary field sizes, but also arbitrary field types. Also, they can contain other things than just text-data, e.g. pictures (like album covers) and other data files. They are prepared to support practically any additions without losing backward compatibility to earlier ID3v2 versions, and they even have support for individuals adding their very own stuff to them too.
  
  
• ID3v1 tags are stored at the end of the mp3-files, while ID3v2 tags are stored at the beginning of them. Storing all such important data at the beginning of files has many advantages. The biggest advantage is that when you are streaming or downloading mp3:s from the internet, you will get all info about them available immediately as the download begins. But there is also sadly one big disadvantage to storing data at the beginning of files. Implementation details of file storage systems on most computer platforms force you to rewrite the whole contents of a file to disk when prepending data to it, while appending data can be done without having to write any additional data than the new one. This means that even if you write e.g. 30 bytes of data to the ID3v2 tag, you might have to write 5 megabytes to the disk. This difference will be especially noticable if the target mp3 is located on a network drive or some other slow medium, and it will be even more noticable in programs processing multiple files in a sequence, like e.g. Mp3/Tag Studio. This is why you might notice a considerable difference between programs/operations writing only ID3v1 tags and programs/operations writing ID3v2 tags. Luckily, a solution (at least in part) to this problem is implemented in the ID3v2 standard too. The first time an ID3v2 tag is written to a file, it can reserve space for possible other ID3v2 data that might be added in the future, so that additional data doesn't have to be prepended, and therefore the file won't have to be rewritten again. When using programs that take advantage of this feature (like e.g. Mp3/Tag Studio), you will most likely only have to rewrite the whole mp3-file the first time you write any ID3v2 data to it. All consecutive writing to the ID3v2 tag will only take about as much time as writing a common appended ID3v1 tag (i.e. no time at all).