title: Should I stop current AVPlayer instance when playing music from another URL?
body: <p>I just created AVPlayer and it plays music well. I have two questions</p>
  
  <ol>
  <li>How to play another music from another URL (should I stop current player?)</li>
  <li>How to show current time of the song in UISlider (actually is it a method that called when the song is playing?)</li>
  </ol>