Is it possible to use the WPF MediaElement to play streaming video from a System.IO.Stream object? The Stream object is being retrieved from a WCF service that stores the media files.
IF you can make the WCF deliver the Media Object via a http-URL (GET) then you can just assign that URL to the MediaElement.Source property - see http://msdn.microsoft.com/en-us/library/system.windows.controls.mediaelement.source.aspx.
For cases where such URL is not available/possible:
Assigning a Stream is currently not possible - although there are some hacks to make that happen, for a DirectShow-based example see http://social.msdn.microsoft.com/forums/en-US/wpf/thread/6191ef1a-0010-4294-a5b4-451bbadca33a/ and http://jmorrill.hjtcentral.com/Home/tabid/428/EntryId/15/WPF-Hackery-Part-I.aspx .
Another option would be to somehow host the Silverlight MediaElement and use the SetSource method which can take a stream and play it... see http://silverlightviewport.codeplex.com/SourceControl/list/changesets and http://msdn.microsoft.com/en-us/library/cc190669%28v=vs.95%29.aspx