There seems to be a lot of trouble with FFMpeg and AVConv packages in Ubuntu and derivatives lately. Instead of delving into why, I’m more interested in how to get one of these fantastic video converters installed on Linux Mint 17.3 so I can get on with my encoding. One of the former PPAs is no longer available, however it is possible to use this one now linked to from the FFMpeg site: https://launchpad.net/~mc3man/+archive/ubuntu/trusty-media

To setup the PPA and install FFMpeg run the following:

sudo add-apt-repository ppa:mc3man/trusty-media
sudo apt-get update
sudo apt-get install ffmpeg

Since Linux Mint 17.* are all based on Ubuntu 14.04 (Trusty), using the trusty PPA will work.