You're referring to the *1 fids and not the actual tags embedded in the files, right?

Yeah, right.

I was asking about the actual tags which I read from mp3's via libid3tag.

Ok.

flac, ogg, etc. don't use ID3 tags, do they?

Ogg uses "vorbis comments" which is basically an array
of name=value pairs where you can use any name you
like. See http://www.xiph.org/ogg/vorbis/doc/v-comment.html

Flac uses vorbis comments natively, but allows id3v1 and
id3v2 frames. The ripper I use doesn't support native flac
(ie vorbis comments) tags, but does support id3v2 , so go
figure ..

wma has text objects which may contain all sorts of tags,
including lyrics. Windows Media Player used to come with
a David Byrne song that had complete lyrics embedded.

If you want to read wma properties you have to use either
the windows-only api, or build your own code from the
specs Microsoft released ... In my case, I stole most of the
code from the mplayer project and from emptool.

Pim