A while back I cross-compiled the ffmpeg and mkvtoolnix packages for my ReadyNas Duo. I have the v1 version, which is a SPARC architecture NAS device running Linux. The details of this are here. Since I was asked for the binaries, I have uploaded them here (tar.gz, 9.8 MB).
To extract:
tar -xzf readynas-ffmpeg-mkvtoolnix.tar.gz
I have tried to figure out which bits are needed for ffmpeg and mkvtoolnix, I basically just copied my /usr/local directory and stripped out stuff I thought belonged to other things I have installed, e.g. transmission and curl. I only copied over to my ReadyNAS the binaries that I needed to get it working for me (remuxing mkv to mp4), so there's probably a bunch of stuff missing. The machine I used to cross-compile likely has these but is a complete mess, so let me know if you get missing libraries and I'll try to search them out.