title: How to play audio in background
body: <p>I use VideoView to play audio from URL.
  My code is as below:</p>
  
  <pre><code>Uri video = Uri.parse(url[i]);
  vv.setVideoURI(video);
  vv.setMediaController(mediaController);
  vv.start();
  </code></pre>
  
  <p>I want to play audio in background.
  How to achieve it?</p>