https://github.com/adaptlearning/adapt_authoring/wiki/Installing-FFmpeg
ffmpeg -i videofile.mp4 audiofile.wav
ffmpeg -i videofile.mp4 -i audiofile.wav -map 0:v -map 1:a -vcodec copy -acodec aac -shortest output.mp4
ffmpeg -i audiofile.wav -codec:a libmp3lame -qscale:a 2 output.mp3