Good discussion and comparison of the HD video spec supported by Silverlight (VC-1) and the recent announcement that Flash would support HD video (H.264):
Recently Flash announced upcoming better video support in the form of H.264. I welcome this change as it will improve vastly on Flash’s and thus the web’s video offerings by far. Obviously this is in response to the Silverlight threat. However there are still some important differences between Silverlight’s video support and Flash’s planned video support.
In this post I discuss just the video aspects of Silverlight versus Flash. If you are interested in the other aspects please see SilverLight, Flash, and SVG
Read the whole thing.