Magnific Popup | Find YouTube anchor link and open it in popup, while also adding additional parameters such as a Playlist ID. Note, this requires magnificPopup JS to be loaded on the page.

magnific-popup-youtube.js

jQuery(window).load(function(){
	// target YouTube anchor links within this ID
	jQuery('#fs-video-playlist a[href*="youtube.com/watch"]').magnificPopup({
		type: 'iframe',
		iframe: {
			markup: '<div class="mfp-iframe-scaler">'+
			'<div class="mfp-close"></div>'+
			'<iframe class="mfp-iframe" frameborder="0" allowfullscreen></iframe>'+
			'</div>', // HTML markup of popup, `mfp-close` will be replaced by the close button

			patterns: {
				youtube: {
					index: 'youtube.com/', // String that detects type of video (in this case YouTube). Simply via url.indexOf(index).

					id: 'v=', // String that splits URL into two parts, second part should be %id%
					// E.g., https://www.youtube.com/watch?v=eU9FruuFxk4
					// Or null - full URL will be returned
					// Or a function that should return %id%, for example:
					// id: function(url) { return 'parsed id'; }

					// we force add a Playlist ID at the end, so that it adds that info to each video. So only use this on videos that should have the Playlist info in it.
					src: '//www.youtube.com/embed/%id%?autoplay=1&rel=0&ytp-pause-overlay=0&modestbranding=1&list=PLpIvLuF2Dh9Z7Rrmoik2vuhaEaFCACfv4' // URL that will be set as a source for iframe.
				},
				vimeo: {
					index: 'vimeo.com/',
					id: '/',
					src: '//player.vimeo.com/video/%id%?autoplay=1'
				},
				gmaps: {
					index: '//maps.google.',
					src: '%id%&output=embed'
				}

				// you may add here more sources

			},

			srcAction: 'iframe_src', // Templating object key. First part defines CSS selector, second attribute. "iframe_src" means: find "iframe" and set attribute "src".
		}
	});      
});