====== Multimedia ======

===== Audio in Video austauschen =====

  ffmpeg -i test.mp4 -vn -acodec copy output-audio.m4a
  #bearbeiten (audacity "Effekt - Kompressor" für Lautstärkeangleichung, leises lauter)
  ffmpeg -i test.mp4 -i output-audio_new.m4a -c:v copy -map 0:v:0 -map 1:a:0 test_new.mp4

===== m4a in mp3 =====

  ffmpeg -i foo.m4a -acodec libmp3lame -aq 2 bar.mp3

https://coderwall.com/p/zbevoq/convert-m4a-to-mp3-with-ffmpeg