Untested method to get percentWatched

gistfile1.txt

var lastTime = 0,
  watchedSecondHash = new Array(Math.floor(wistiaEmbed.duration()));
wistiaEmbed.bind("timechange", function(t) {
  var totalSecondsWatched = 0, percentWatched;
  watchedSecondHash[Math.floor(t)] = true;
  for(var i=0; i < watchedSecondHash.length; i++) {
    if (watchedSecondHash[i]) {
      totalSecondsWatched++;
    }
  }
  percentWatched = totalSecondsWatched / watchedSecondHash.length;
});

slight change in calculating the pecentWatched... used duration instead of the hash length (was always the same as the total seconds watched):

percentWatched = totalSecondsWatched / wistiaEmbed.duration();