In your dashboard you can enable the option for your community admins and users to add videos to content descriptions (posts, events and library items). This article gives you information on how this content affects any of your external websites.
Embedded videos consist out of two parts:
A parent 'div' with the CSS class 'embedded-video-wrapper'
An 'iframe' that contains the video link and has the CSS class 'embedded-video'
On your website, the two CSS classes can be used to style the videos to your liking. Below you can find an HTML example of a description with an embedded video.