title: Joining MP3's via commandline with background track
body: <p>I'm already taking advatage of two command line utilities. I'm using ffmpeg to convert m4a to mp3, and then I'm combining a few mp3's into one large one using mp3wrap. The resulting file is something like this:</p>
  
  <pre><code>BackgroundMusic.mp3 &gt; Audio1.mp3 &gt; Audio2.mp3
  </code></pre>
  
  <p>I need something more like</p>
  
  <pre><code>Audio1.mp3 &gt; Audio2.mp3
  |_____________________|
             |
    BackgroundMusic.mp3
  </code></pre>
  
  <p>To where the background music runs continuously in the background. Would be nice to be able to change the volume of each track too.</p>
  
  <p>Does anyone know a command line program like mp3wrap but can also add in a background track?</p>
  
  <p>I will not be able to use a GUI program such as Audacity, as all of this will be automated on the server.</p>
  
  <p>Thanks!</p>