FFmpeg is a free and open-source software suite of libraries and programs for handling video, audio, and other multimedia files and streams. The FFmpeg program itself is a software-based processor for video and audio files, that can be used for transcoding various video and audio files between different formats, for very basic editing (trimming in and out, joining two video or audio pieces), for scaling videos, and a few other tasks. FFmpeg includes codecs for most audio and video file formats and is therefore very useful for the transcoding of common and uncommon media files. FFmpeg has a command line interface which may scare off the less brave amongst us, but the commands are well documented on the web site and once you get the hang of it, you will not regret having taught yourself how to run FFmpeg. The flexibility of the command line interface allows at the same time a great accuracy and complexity in video and audio manipulations, while the software itself runs incredibly fast, making huge tasks easy and quick. There are a number of (free) GUI implementations of FFmpeg but it ‘s more fun to take a little time and teach yourself how to use the command line interface.
Free for all operating systems on https://ffmpeg.org/