For various reasons, I'm thinking about making the switch from LAME-APS to AAC@192 w/ iTunes, and I've been doing research, but I can't seem to find a straight answer on what tagging formats I can use with AAC. I use ID3v2.3 with my MP3s, but that of course isn't universally recognized, and I'm always a bit wary when writing new tags because of how it has to re-write the whole file.

From the few dozen files I've bought from iTunes Music Store, it seems whatever tag Apple applies comes with all the essential fields plus album art (which I don't use). What tag format is that, where is it placed within the file (beginning or end), how easy is it to modify, and does iTunes display all the fields it supports, or are there others?

And what other tag formats could I use? I've heard some rumblings about APEv2, but not enough to get a coherent sense of how useful they are. I know I'm asking a lot of questions, but I'm just trying to do as much research as possible so I make the right choice. (And of course, I'll probably end up changing my mind after a month anyway. )

The only fields I really care about are:
Artist, Title, Album, Track #/Total # Tracks (5/16), Year, Genre, Composer, and Disc #/Total # Discs. That last one's critical, and probably a deal-breaker. ID3v2 calls it "Position in Media Set", and iTunes AAC calls it "Disc." Fields like ID3v2's Orchestra, Conductor, Comment, Remixed by, and Lyrics might be useful to me in the future, but I don't use any of them now.

Apple has pretty much defined the standard for MPEG-4 AAC tags with their iTunes tagging format for AAC. I don't even know if you can call it a standard since no official specifications for the tags have been released by Apple. MPEG-4 AAC just didn't have any tagging format so Apple created one. I hear the MPEG group is coming up with a tagging format in the MPEG-7 standard but I'm not really familiar with that. Almost all programs read the Apple-compatible tags from MPEG-4 AAC files so using another tagging format will not get you much compatibility. I'm not even aware of any other tagging format designed specifically for MPEG-4 AAC.

For various reasons, I would advise you to use the iTunes tag.

There is no AAC tagging standard. Therefore there's no guarantee that your tags will work with the future devices. If you tag with Apple's standard you should not have issues with anything Apple.

However using ID3 tags or APE tags on AAC files would make the situation much worse IMHO. Then your files could be recognized with a handful of software.

Everything boils down to on what hardware+software you intend to play your files.

Ah, that answers that question. The Apple tag seems to do everything I need it do (including the blessed Disc tag), so I see no reason not to use it. Thanks. That said, can anyone recommend a (hopefully freeware) program that would make editing such tags less cumbersome than iTunes' slow Windows interface, one at a time? Tag & Rename looks good, but isn't free.

foobar2000 and its freedb component should do exactly what you want and more (match albums and tag your files automatically). Also if you just want to edit tags by hand foobar2000's foo_infobox component serves me very well.

Wait a second, I just thought of something. If no one but Apple knows what the specs for their proprietary tag format are, how were the developers of Tag & Rename able to incorporate it into their program? Same question with foobar.

It is easy to open a file in hex editor and see how it is done. The most complete documentation can be found here.

iTunes does that as well (albeit w/ CDDB)

Am I wrong, or are MP4 tags all except Apple's property? Isn't MP4 tags a part of the MP4 container, which are both documented?

Everybody uses Apple's tags nowadays. There is mpeg-7 which defines real metadata in mp4 but nobody uses it.

Some further information regarding ACC fields and their MP3 counter parts:

iTunes AAC tagging


Another free tag editor that does AAC tagging is TGF:

TGF tagger


BTW iTunes do allow the tags of multiple songs to be updated in one go. Just select more songs before beginning the edit.

indeed, i also read somewhere that mpeg-7 also allows to use "private tagging" formats (as apple tags) via a "meta" atom (same level as "udta" in .mp4)

so storing the apple tags in a "meta" rather than the "udta" atom might be more compliant to the mpeg standard, but i dunno more