We just introduced SilverSuite for Silverlight 3 with MPEG4.2, RTSP and Flash FLV support. So you can now play RTSP streams and Flash Video streams from your Silverlight applications. The component comes with full source code to the MediaStreamSource classes and therefore allows you to extend or customize them individually. Also included is a policy server and proxy server, that takes care of your cross domain access restrictions if necessary. Check out the demo