If you convert audio or video files you will need FFmpeg library. For example, when I installed the program Flacon to work with flac files, the software required to install FFmpeg.
Now I'll show you how to install this library. It is very simple.
Installation latest version into Linux Mint:
sudo apt-get install ffmpeg
If the package is missing, add the repository and install again
sudo add-apt-repository ppa:mc3man/trusty-media sudo apt-get update sudo apt-get install ffmpeg
Do not forget from time to time to update the build FFmpeg to keep the library up to date. Just update your system through Update Manager as usual.