title: How to use PreparedAsync In ExoPlayer
body: <p>I have an application that uses ExoPlayer. But it's done so before the start, I need to know Prepared is already ready or not.</p>
  
  <p>I can not find PreparedAsync in ExoPlayer. Therefore, the application crashes</p>
  
  <p>Running and training is 2 different things.</p>
  
  <p>I need to find out when the preparation is over, To get the length of the video track.</p>
  
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  <p>I need any suggestions. Already 4 days I rack my brains. Help Developers ((</p>