title: How to set current playback duration and elapsed time on iOS 7 lockscreen?
body: <p>Starting from iOS 5, every music player can set current playing music information such as title, artist, album title, and artwork on [MPNowPlayingInfoCenter defaultCenter].nowPlayingInfo to show on lock screen.</p>
  
  <p>On iOS 7, playback position slider, duration, and elapsed time information are added to both lock screen and control center. However, I cannot find any documents to set these kinds of information and enable the slider to change playback position.</p>
  
  <p>Is there any way to solve this problem?</p>