No metadata extraction in MediaExport plugin

I'm using Ubuntu Server 12.10 (no desktop, headless) together with rygel updates ppa ppa:yg-jensge/gupnp. (Same thing happens with gupnp-unstable ppa)

I installed rygel and adapted rygel.conf to my needs. Basically I enabled the MediaExport plugin with extract-metadata=true.
I can see the server library on my Android phone using Bubblepnp and also playing music works. All seems to be working.

BUT: in the library under "Music" I only have an "ALL" folder listing all filenames, all with "Unknown Artist". I'm pretty sure that at least some of my mp3 have some metadata, but nothing seems to get extracted and therefore nothing is in the library under Artist/Genre etc.

I'm using Ubuntu 12.10 together with the same rygel on my notebook and it works fine with metadata. But here I'm using Gnome etc. What I suspect is that some dependencies for metadata extraction during rygel install on the Ubuntu Server are not installed.

(Rygel was also the first "audio" tool I installed on a fresh Ubuntu 12.10 Server install. So there was no Alsa nor gstreamer stuff installed beforehand. Only what rygel installed as its own dependencies). On my Ubuntu Server there is no Desktop installed as I'm using it headless.

So what is necessary for MediaExport plugin to extract metadata (from mp3)? I didn't install tracker (and rygel-tracker) as it installs some X11 and gnome stuff. I think MediaExport uses other tools to get the metadata..

Thank you for your help!
steffen