Handbrake is a free, open source software tool that allows you to convert one video format to another. It is available for Mac, PC, and Linux platforms at handbrake.fr.
Handbrake Installation Notes
In order to run on a PC, Handbrake requires Microsoft .NET Desktop Runtime 6.0. After installing Handbrake on a PC, you may be prompted to install Microsoft .NET Desktop Runtime if it is not already installed on your computer. If the application fails to open when clicked, try manually installing it. See the Installing on Windows section of the Handbrake Documentation page for links and instructions.