To add to the list of ideas - if you have an API to call to pause the player (instead of destroying the page/RadWindow), you can do that in the OnClientClose event instead. In case you are using a content page, you can call a function in it, as shown in this article: http://www.telerik.com/help/aspnet-ajax/window-programming-calling-functions.html.
Regards,
Marin Bratanov
Telerik
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