Jon, If you look at DirectFB-0.9.9-r2.ebuild, you'll see that if the mpeg flag is set, it fetches the libmpeg3 libraries, unpacks them in WORKDIR, compiles libmpeg3, then points DirectFB to that source tree. The thing is I have hacked through libmpeg3's ebuild, with various patches to have it install nicely into /usr/include and /usr/include/{audio,video}, and ideally, I would rather use that to have DirectFB have libmpeg3 support in it. Please see if you can sort that out for me.
bleh, I sorted this one out