Sound TIME

Good day everyone here I have a new thread, now is about a sound, I have this code that shows the time from a sound and this is increasing the time from let’s say 0:00, 0:01, 0:02…4:30. Now my question is how can I trick it to do the opossite, meaning that the code to show the time left like 4:30, 4:29, 4:28…0:03, 0:02, 0:01.


onEnterFrame = function ()  {   _global.timer =  int(podcast_sound.duration/1000);
_global.position =  int(podcast_sound.position/1000);   
   setTime = {};
   setTime.minutes =  int((_global.position)/60);
   setTime.seconds =   int((_global.position)%60);
   setTime.total =  checkDigits(setTime.minutes)+":"+ checkDigits(setTime.seconds);
  //  setTime.total = checkDigits((timer)%60);
timeDisplay.text =  setTime.total;
}   function checkDigits(pWert) {
   return (pWert<10) ?  pWert="0"+pWert : pWert;
}