Facebook custom conversion based on time such as a video playing

fbcustom.js

<script>
const VideoLenSeconds = 300;  // Modify this to the length of your video in seconds. 300 = 5 mins
const Divisions       = 10;   // 10 = every 10%, 4 = every 25%, 5 = every 20%
const ConversionPct   = 75;   // Set this to record a desired conversion percentage

// Don't change these!
const MSecsPerSecond  = 1000;
var percentageViewed  = 0;
var converted         = false;

function VSLconvert()
{
  percentageViewed++;
  str = "";
  var FractionViewed = Math.round(percentageViewed / Divisions * 100);
  str = FractionViewed + "%";
  if(percentageViewed <= Divisions) // If they just stay on the page past video time, don't fire more events
  {
    fbq('trackCustom', 'VSLViewed', {viewed: str});
    if(FractionViewed >= ConversionPct)
    {
      if(!converted)
      {
        converted = true;
        // This is the custom conversion event to optimize for
        fbq('trackCustom', 'VSLConverted');
      }
    }
  }
  else // They've watched it all. Stop the timer
  {
    clearInterval(vslTimer);
  }
}
// Fires every specified % of video
var vslTimer = setInterval(VSLconvert, VideoLenSeconds * MSecsPerSecond / Divisions);
</script>