move = function(event) {
  if (window.sliderDown) {
    var x = event.clientX || event.touches[0].clientX;
    var startX = window.innerWidth * 0.05;
    var layerX = x - startX;
    var per = Math.min(1, Math.max(0, layerX / parseFloat(barEmpty.scrollWidth)));
    player.volume(per);
  }
}
Format the time from seconds to M:SS.
@param  {Number} secs Seconds to format.
@return {String}      Formatted time.