Rocket.Chat/packages/rocketchat-oembed/client/oembedYoutubeWidget.html

<template name="oembedYoutubeWidget">
	{{#if parsedUrl}}
		<blockquote class="background-transparent-darker-before">
			<a href="{{url}}" target="_blank">{{parsedUrl.host}}</a>
			{{#if collapsed}}
				<span class="collapse-switch icon-right-dir" data-index="{{index}}" data-collapsed="{{collapsed}}"></span><br>
			{{else}}
				<span class="collapse-switch icon-down-dir" data-index="{{index}}" data-collapsed="{{collapsed}}"></span><br>
				<iframe width="355" height="200" src="{{meta.twitterPlayer}}" frameborder="0" allowfullscreen></iframe><br>
				{{{meta.description}}}
			{{/if}}
		</blockquote>
	{{/if}}
</template>