This is very annoying that ffmpeg is missing from Linux Mint! They have ffmpeg2theora which is a totally different codec and does not work as ffmpeg does at all (it is basically totally different).
However on Linux Mint 17 I was able to use a Ubuntu PPA and sucessfully install ffmpeg!
https://launchpad.net/~mc3man/+archive/ubuntu/trusty-media
Adding this PPA to your system........