For building gtkpod in flavors:
mp4v2: library used by gtkpod for m4a/aac support
libgpod: required support libraries for gtkpod
gtkpod-lite: stock gtkpod with no extra codec support. Just mp3.
gtkpod: full version of gtkpod, including m4a support (mp4v2 library). Also a slew of other libs supported, so this one has a big footprint.
If you're interested, get the attached script files (4).