Microsoft said on Tuesday that the next version of its Silverlight media player, due early next year, will be able to play live high-definition video encoded for rival Adobe Systems' Flash player.

Users of Silverlight 3 will also be able to listen to streaming music encoded in the same format used by Apple's iTunes player.

Adding support for the H.264 video compression formats based on the increasingly popular MPEG-4 standard won't necessarily make Silverlight-viewed video look better.

Nor will supporting the Advanced Audio Coding (AAC) codec allow Silverlight to play music stored locally by iTunes, due in part to Apple Inc.'s restrictions, said Steven Sklepowich, group product manager for Silverlight Media.

But it will prepare Silverlight 3, which will ship in the first quarter of next year, to play a much wider variety of the streamed HD video and high-fidelity music that broadcasters are expected to bring online.

"We are becoming more of an open runtime environment," Sklepowich said.

Silverlight is a Web browser plug-in that allows users to watch or listen to streaming multimedia. It differs from Microsoft's Windows Media Player, which is mostly used to play back media already downloaded off the Internet.

When Microsoft first released Silverlight last year, to compete with Flash, it required broadcasters to encode video in the VC-1 codec, a now-open standard for HD DVDs and Blu-ray Discs based on Windows Media formats.

VC-1 enabled true DVD-quality streaming video that is much higher quality than the Flash video on sites such as YouTube, where most of the videos are still encoded in the H.263 codec. Such files are streamed to Web browsers, which cache them as .flv files.

Adobe has since updated its Flash 9 player to play HD H.264 video files, which are stored temporarily as .f4v files. Both .f4v and .flv are different than .swf files, which can be downloaded and played by Flash offline (Silverlight today plays streamed video in the .asf file container format.)

Silverlight 3 won't be able to play .flv or .swf content, said Sklepowich. But it will be able to play H.264-based .f4v content.

Microsoft had long resisted calls to make its Silverlight player more compatible with Adobe's. Adobe says that last year 70 percent of Web video was streamed via Flash's .flv format.