You cannot control the MediaElement in silverlight. So in order to achieve this you should create class like WPF WriteableBitmap and manually update it to create some kind of visualization.
Also you should modify the control template to hide the media element and add some Image control that will show you dynamically updated visualization.
I'm not aware of the performance of this approach. I'm not sure if this is achievable.
You could read more about WriteableBitmap for Silverlight (custom implementation) here:
All the best,
the Telerik team
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