Small javascript for playing/pausing the video when in/out of the viewport

isVideoPlayerVisible.js

var videos = document.getElementsByTagName("video");

function checkViewport () {
  for (var i = 0; i < videos.length; i++) {
    var video = videos[i];
    var x = video.offsetLeft,
        y = video.offsetTop,
        w = video.offsetWidth,
        h = video.offsetHeight,
        r = x + w,
        b = y + h,
        visibleX,
        visibleY,
        visible;

    visibleX = Math.max(0, Math.min(w, window.pageXOffset + window.innerWidth - x, r - window.pageXOffset));
    visibleY = Math.max(0, Math.min(h, window.pageYOffset + window.innerHeight - y, b - window.pageYOffset));
    visible = visibleX * visibleY / (w * h);

    if (visible > 0.5) {
      video.play();
    } else {
      video.pause();
    }
  }
}

window.addEventListener('scroll', checkViewport, false);
window.addEventListener('resize', checkViewport, false);