title: converting all the mp4 audio files in a folder to mp3 using ffmpeg
body: <p>how can I convert all of the <code>mp4</code> files in a given folder to <code>mp3</code> using ffmpeg.
  Almost all of the links I have seen on google is all about converting mp4 video to mp3.
  I can do this via VLC player but I have got huge collection ~ 1000 mp4 audio files and want this to be done over command line by some script or command.
  Is it possible to do it via gstreamer?</p>