title: Tracking stop playing Audio event?
body: <p>I am tracking events in Analytics, but I have a question with audio tag.
  I can track when the audio tag is played, but I don't know how to track how long the audio track has been played.
  Did the user listen it all ?
  Or how long did he listened it ?
  Curently I used onclick=" ga('send', 'event', 'Audio', 'play', 'Lecture');"
  But what will it be to know how long it has been listened to?
  thanks for your help !</p>