Microsoft was motivated to support H.264 because it is becoming "the next-generation standard," said Sklepowich, with HD digital broadcasters such as DirecTV and Dish Network using H.264.
Adding H.264 support will cut work for broadcasters who previously would have had to do the time-consuming work of re-encoding their video in VC-1 to support Silverlight, he said.
And that should encourage more of them to stream video using Silverlight, as well as build special Silverlight-based players such as the ones specially created for NBCOlympics.com and the Democratic National Convention. The players, in addition to showing HD video, also offer features such as picture-in-picture, multiple views, and ticking data, Sklepowich said.
Microsoft plans to show off an early preview of Silverlight 3 at the International Broadcasting Conference (IBC) 2008 in Amsterdam later this week, according to Scott Guthrie, corporate vice-president of Microsoft's Developer Division.
A beta of Silverlight 3 is expected soon after Silverlight 2 ships this fall, Sklepowich said.
The other caveat on video is that Silverlight will only be able to view .f4v streamed video if it is delivered from Web servers using the standard http: protocol, Sklepowich said. Video delivered from Adobe's Flash Media Server software using its proprietary RTMP protocol won't play, he said.
Silverlight 3 will enable users to listen to streamed music in AAC formats, in addition to its existing support for MP3 and Windows Media Audio (WMA) streaming. WMA is the most popular format for streaming today.
AAC is best known as the default audio format used by Apple Inc.'s iTunes, iPod and iPhone to store music files on devices and/or PCs.
Silverlight 3 will not be able to play those stored songs, Sklepowich said, partly because Apple adds its own DRM (digital rights-management) technology called Fairplay to prevent non-iTunes programs from playing them, and partly because Silverlight is meant only for streaming content.
However, an increasing number of broadcasters are using AAC to stream music through the Web, which Silverlight will be able to play.