The streaming video Web site for last month's Beijing Olympics, NBCOlympics.com, was a technological success for NBC Sports and its close partner Microsoft. But it was a missed monetary opportunity for the broadcaster, which succeeded perhaps too well in protecting the interests of its primetime TV advertisers.

According to information released by Microsoft on Tuesday, NBCOlympics.com received 42 million unique visitors, delivered 56 million high-def video streams using Microsoft's Silverlight technology, and received 6 million visits from users of mobile phones and other devices.

Microsoft built a special Silverlight-powered player for NBCOlympics.com that let viewers watch DVD-quality video, see up to four events simultaneously, and read and surf other related information. Despite occasionally-heavy usage during the two week event, there were no reports of outages, or delays in video delivery or from the Internet.

The average viewing time at the site, which is still up, was 27 minutes, according to Scott Guthrie, corporate vice-president of Microsoft's Developer Division.

Also, by requiring viewers to download Silverlight, the site helped Microsoft add about 20 million new Silverlight users, reports the Reuters news agency.

Microsoft is trying hard to make inroads against the dominant Flash player from Adobe Systems Inc., which the vendor says is installed on 99% of PCs in developed countries.

NBCOlympics.com probably would have attracted many more visitors - and helped Microsoft better spread Silverlight – if NBC had not delayed or limited the availability of Olympics footage online for popular events so as not to hurt US viewership of its tape-delayed primetime broadcasts, which were typically shown half a day after the events happened in Beijing.

Appeasing its TV advertisers likely hurt its online advertising revenue, too. Research firm eMarketer Inc. estimated that NBCOlympics.com generated only US$5.75 million in online video ad revenue.

In contrast, CBS is reported to have made $23 million in online ad revenue from streaming every one of the NCAA's March Madness basketball tournament games live earlier this year.

Some blogs noted last week that NBC is still using Adobe Systems Inc.'s Flash for its new NFL live video streaming site, rather than Silverlight.

The decision was the NFL's not NBC's, wrote Chris Carper, a director on the Microsoft Silverlight team, citing an Adobe press release.

"To say, Silverlight was dumped by NBC, or forgotten by NBC is unfortunately an effort to drive more views and [to be honest], just poor journalism," Carper wrote.

Silicon Alley Insider's critique of the NFL site: the video was "pixelated and jumpy, and there's no full-screen mode. But there were some cool features, such as a 'star cam' trained on individual players."

More recently, Silverlight was used to stream 350,000 hours of video from last month's Democratic National Convention to viewers through the Web, Guthrie said.

The DemConvention.com site overall received 3.2 million visits and 2.6 billion hits during the Convention week, according to the Democratic National Convention Committee Inc.