Rocket.Chat/app/oembed/client/oembedVideoWidget.html

<template name="oembedVideoWidget">
{{#if parsedUrl}}
	<blockquote class="message-oembed background-transparent-darker-before">
		<div><a href="{{url}}" rel="noopener noreferrer" target="_blank">{{parsedUrl.host}}</a></div>
		<span>{{title}}</span>
		{{#if collapsed}}
			<span class="collapse-switch icon-right-dir" data-index="{{index}}" data-collapsed="{{collapsed}}"></span>
		{{else}}
			<span class="collapse-switch icon-down-dir" data-index="{{index}}" data-collapsed="{{collapsed}}"></span><br/>
			<video controls class="inline-video">
				<source src="{{url}}" rel="noopener noreferrer" type="{{contentType}}">
				Your browser does not support the video element.
			</video>
		{{/if}}
	</blockquote>
{{/if}}
</template>