getDuration(element, document) {
		const duration = {
			in: undefined,
			out: undefined,
			time: undefined,
		};
		if (element.tagName === 'multitrack') {
			const lastTrack = element.childNodes.item(element.childElementCount - 1);
			const playlist = document.getElementById(lastTrack.getAttribute('producer'));
			duration.time = playlist.childNodes.item(0).getAttribute('length');
			if (duration.time === null)
				duration.time = this.getDuration(playlist.childNodes.item(playlist.childElementCount - 1), document).time;
			else
				duration.time = timeManager.addDuration(duration.time, this.getDuration(playlist.childNodes.item(playlist.childElementCount - 1), document).time);
		}
		else {
			if (element.tagName === 'track') {
				const playlist = document.getElementById(element.getAttribute('producer'));
				element = playlist.getElementsByTagName('entry').item(0);
			}

			duration.in = element.getAttribute('in');
			duration.out = element.getAttribute('out');

			if (duration.in === null) {
				duration.in = '00:00:00,000';
			}

			if (duration.out === null) {
				const producer = document.getElementById(element.getAttribute('producer'));
				const properties = producer.getElementsByTagName('property');
				for (let property of properties) {
					if (property.getAttribute('name') === 'length') duration.out = property.innerHTML;
				}
			}

			if (duration.in > duration.out) throw(`Attribute in is greater than out: ${element.outerHTML}`);

			duration.time = timeManager.subDuration(duration.out, duration.in);
		}
		return duration;
	}
Get in, out and duration of timeline item

@param {Element} element
@param {Document} document
@return {{in: string, time: string, out: string}}