Hurley and Chen hope to work more closely with copyright holders to convince them they can stimulate more interest in their material by sharing snippets on YouTube. That message seems to be resonating. Some movie studios are now posting clips on YouTube as part of their marketing campaigns.

In a nod to copyrights, YouTube recently imposed a 10-minute limit on all videos, figuring that time restriction will lessen the likelihood of massive infringement.

Not much has slowed YouTube since last May, when Chen debuted the site's first video — a clip of his cat, "Pajamas," pawing at a dangling string.

In February, YouTube attracted 9 million unique U.S. visitors, ranking it just behind MSN Video (9.3 million visitors)and ahead of Google Video (6.3 million visitors), according to Nielsen/NetRatings Inc.

In a more telling indication of video supremacy, YouTube's U.S. visitors viewed 176 million pages in February while the video audiences at MSN and Google viewed 38 million and 76 million pages, respectively, Nielsen/NetRatings said.

The next major test for YouTube figures to come during the next few months, when Hurley and Chen hope to make money by selling video ads on the site. For now, the 25-employee company is subsisting on $11.5 million invested by Sequoia Capital, the same Menlo Park venture capital firm that helped launch Google.

Much like Google with its search engine, YouTube conceivably could display ads hawking a product or service related to whatever video is being watched. The company already is talking to a convenience store chain about an advertising campaign that might launch in June.

YouTube's advertising aspirations might increase pressure to prevent pornographic videos from popping up on the site. Posting porn on the site violates YouTube's policy, but that hasn't stopped abuses. Depending largely on complaints from its users, YouTube aggressively removes offending material, but not before thousands of people watch the videos.

During a recent tour of YouTube, The Associated Press found videos of strip-teasing women as well as clips of graphic sex scenes promoting other pornographic sites.

Besides scaring off advertisers, YouTube's vulnerability to porn risks infuriating parents if they discover that sexually explicit videos are accessible to minors frequenting the site, said Greg Kostello, chief executive of vMix, one of the many video sites trying to catch up to YouTube. Kostello said he also has found videos of violent beheadings on YouTube. Unlike YouTube, Kostello said vMix uses filters to keep out pornography and other inappropriate material.

"I can't imagine my kids coming to a site and seeing some of the porn and hateful commentary that shows up on YouTube on an almost daily basis," said Kostello, a former executive with Vivendi-Universal. "And if you are an advertiser, you aren't going to be happy if porn shows up by one of your ads."

Hurley and Chen believe their community policing system is highly effective, pointing to similar practices used by online auctioneer eBay Inc. and Internet advertising service Craigslist. YouTube's technology also blocks repeat offenders from posting videos.

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