title: How to get the duration of an audio file in flutter?
body: <p>I am trying to get the duration of an audio file and set it to a <code>String</code>. I am using <code>flutter_sound</code> plugin to play the sound. <code>onPlayerStateChanged</code> listen has duration but I don't know how to use it to set a <code>String</code> to duration value without playing the sound.</p>
  
  <p>The main aim is I want to select an audio file which has a Max length of 20 sec. Can anyone please help me solve it?</p>