FFmpeg is a free software, and a multi-platform solution for video, audio, and
other multimedia files and streams. It is a terminal software, but there are
graphical options like QwinFF [http://qwinff.github.io/], Avanti
[http://www.avanti.arrozcru.org/], FFmpegYAG
[https://sourceforge.net/projects/ffmpegyag/] or Axiom
[https://github.