Will Silverlight support all the codecs that Windows Media Player supports?
Silverlight supports the most commonly used codecs from the Windows Media format that are also supported in Windows Media Player. This includes WMV and WMA. Since Silverlight is a lightweight, cross-platform technology, it only supports the codecs that are most commonly needed for Web playback. Microsoft has announced native support for MP4 formats (H.264/MPEG AVC video and AAC audio) in a future version of Silverlight and we will continue to gather feedback from customers about additional required format support.