ok, i plan to finish the xmms-aac plugin in 3-4 days, but to have a clean code. I would like to avoide the horrible hack of the ID3tag len header..

i just copy on the winamp plugin. But it's not very... clean... is the id3lib have a function to retreive the len of the id3tag ??

Also i would like to know where can i have information about AAC structure format (i won't read all faad2 source code) to enable seeking without reading whole file (because if you play an aac file on a network... you read around 3Mo+ before the plugin sound something... not very cool in this case)

The info about the headers can be found on the AAC pages at the wiki page: http://www.audiocoding.com/wiki.
I think you's can better use that "dirty hack" for finding the id3 tag length than the id3lib library itself. It will find the length in the exact same way and if you ask me id3lib is much more dirty than most other code I have ever seen.

Menno