After converting a bunch of cd files from wav (created by cdparanoia) to m4a (using soundKonverter) I'm unable to edit the tags in Amarok. Whereas with the mp3 files I've created with soundKonverter seem to work. Is this a known/comming issue with m4a? Is m4a support a new feature for Amarok?

Lastly, are m4a files typically smaller than mp3 files (of the same track) ?

m4a (aac) has been supported with plugins since Dapper... but it was always a pain at that point to make sure you had the right ones and even then, I remember fighting with it. 

I too have issues with Tagging m4a in linux in general [I use kubuntu 7.10 now], and have to use a program called exfalso.  It works but the interface lets you only do one file at a time.  Kind of a pain if your files are in different folders.  You could also run itunes 6 [has to be 6, as I think the 7 doesn't run still] with wine.  That is kind of clunky and slow in it's own right.

fwiw I'm also using Ex Falso and as of version 1.0-1 you can edit multiple files at once.

I had the same problems with hundreds of mp4 and m4a files...I finally gave in and transcoded them to mp3 using PAPCL convert Amarok script (and oommand line uptil)... (I know, lossy->lossy ...sounds the same to me on my mp3 player and through my headphones)

This was posted a while ago, but I thought I'd add this since there was no answer given.

The ability to edit m4a/mp4 tags is not enabled by default in the Amarok binaries that most distributions provide. If you're using Ubuntu Hardy (8.04) you can add the Medibuntu repository, which has a version of Amarok compiled with libmp4v2 support. If you're using Intrpid, then tough luck I'm afraid. The Medibuntu guys told me that there's a bug somewhere in Amarok 1.4.10 that prevents it from being compiled with libmp4v2 support.

Bottom line: Stick with Hardy and install Amarok from Medibuntu. If you're on Intrepid, then try to compile it yourself, if you can figure out how. I tried. I failed.

I do understand why there's such political **** around 'non-free' features, weird licenses and closed code. But after two months of having to use yet another bloody application when one would do, I'm really f*cked off. I'd move to Banshee, JuK or Rhythmbox if any of them could read the 'Comments' tag. But they don't for some completely unknown and mysterious reason.