Video play on scroll

video-on-scroll.js

var video = document.getElementById('hero_video');
var video_wrapper = document.getElementById('mc-hero');
var videoStart = video_wrapper.offsetTop;

var target = 0,
    current = 0,
    easeAmount = 0.05;

function scrollVideo() {
  var videoLength = video.duration,
      scrollPosition = document.documentElement.scrollTop || document.body.scrollTop;

  if (scrollPosition >= videoStart) {
    target = ((scrollPosition - videoStart) / (8289 - window.innerHeight)) * videoLength;
  }
}

function ease(current, target, easeAmount) {
  return current + (target - current) * easeAmount;
}

function animate() {
  current = ease(current, target, easeAmount);

  if(video.readyState >= video.HAVE_FUTURE_DATA) {
    video.currentTime = current;
  }

  requestAnimationFrame(animate);
}

window.onscroll = function() {
  scrollVideo();
};

animate();