title: Python .avi to .mp4
body: <p>I need some python code for this function. I have installed ffmpeg in Ubuntu. </p>
  
  <pre><code>def convert_avi_to_mp4(avi_file.avi):
     mp4_file = None
     #some code to do the job
     return mp4_file
  </code></pre>
  
  <p>Thank you</p>