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

<template name="oembedYoutubeWidget">
	{{#if parsedUrl}}
		<blockquote>
			<a href="{{url}}">{{parsedUrl.host}}</a><br>
			<iframe width="355" height="200" src="{{meta.twitterPlayer}}" frameborder="0" allowfullscreen></iframe><br>
			{{{meta.description}}}
		</blockquote>
	{{/if}}
</template>