If you look at the current video detail template, you can see that the control for that is called MediaPlayerControl and you can add it in any ascx markup:
"server" MediaContentId="Guid of the video"
You need to register your prefix like this:
<%@ Register TagPrefix="sf" Namespace="Telerik.Sitefinity.Modules.Libraries.Web.UI.Videos" Assembly="Telerik.Sitefinity" %>
Also if you add a property of type GUID to bind to, you can easily add a friendly UI selector for that by generating a designer using Thunder, it is capable of adding your video selector for the back-end edit screen of the widget. Follow the docs here
for more information.
Hope this helps!
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