Do you think Silverlight media features are built on top of Windows Media Player?
The Silverlight browser plug-in is a separate component, independent of Windows Media Player. Silverlight is designed for delivery of cross-platform, cross-browser media experiences and rich interactive applications (RIAs) inside a Web browser combining audio, video, animation, overlays, and more. Windows Media Player delivers a breadth of local playback and user focused experiences. You don’t require Windows Media Player to be installed on PC to run Silverlight applications. Silverlight is completely independent and when installed is less than 2 MB in size.
Silverlight supports Windows Media Audio and Video (WMA, WMV7–9) and VC-1, as well as MP3 audio. Additional formats may be available over time.