title: Detect pause/resume in ExoPlayer
body: <p>I searched two days for this question in <a href="https://github.com/google/ExoPlayer/issues" rel="noreferrer">github</a> but i can't find true answer . I want example for detecting <code>pause / resume</code> in <code>ExoPlayer &gt; 2.x</code> . 
  Any one can give me an example ? I checked <code>onPlayerStateChanged</code> and problem not solved .</p>
  
  <pre><code>onPlayerStateChanged   :   STATE_BUFFERING 
  onPlayerStateChanged   :   STATE_READY 
  </code></pre>
  
  <p>I just got this log from <code>onPlayerStateChanged</code> and this is not called in all times !</p>