Either use libav instead of ffmpeg or use the meta-multimedia layer in OE when it gets created. This will involve adapting Mediatomb to work with libav as it does not yet do this out of the box; Ubuntu already has a patch: https://bugs.launchpad.net/ubuntu/+source/mediatomb/+bug/784431 At the same time we should be able to remove libgsm and faac as they should not be needed for Baryon.
This may be obviated by bug 4748.
libav is now in OE-Core, mediatomb in meta-baryon has been fixed to support it, and ffmpeg has been dropped. I think we can call this resolved.