var mediaelement = document.querySelector('video');
	mediaelement.addEventListener('progress', function() {
        var range = 0;
        var bf = this.buffered;
        var time = this.currentTime;

        while(!(bf.start(range) <= time && time <= bf.end(range))) {
            range += 1;
        }

        var loadStartPercentage = bf.start(range) / this.duration;
        var loadEndPercentage = bf.end(range) / this.duration;
        var loadPercentage = loadEndPercentage - loadStartPercentage;
    });