IN RECENT months, long-time users of video-sharing website YouTube have noticed that the Google-owned site's definition of acceptable content has narrowed considerably.
In addition to its longstanding campaign to crack down on illegally copied material, in September the site outlawed videos depicting drug abuse and last week tightened its guidelines further to restrict profanity and sexually suggestive content.
In other words, before the money wagons roll in, some law and order needs to be imposed.
The four-year-old site, long a cultural frontier complete with virtual vice and chicanery, is growing up. TV shows and feature films have arrived, and so even has US president-elect Barack Obama, who uploads his fireside video blogs every week.
"In the last six months, we've been iterating very, very quickly," said YouTube spokesman Ricardo Reyes, adding that as the site becomes more sophisticated, the potential to boost advertising grows too.
YouTube, which costs nothing to use, boasts hundreds of millions of visitors every month, and it has been working to translate more of that activity into profit. "I think that generally people understand that we have to find a way to pay for the service," Mr Reyes said.
Videos that YouTube considers objectionable will no longer qualify for its daily pages, where the most widely viewed clips are showcased. These "browse" pages often act as a kind of viral launch pad, from which many of the web's most-watched videos blast off.
Exile from these areas, while not explicit censorship, cuts deeply into a video's chances of getting noticed.
Reese Leysen, a member of iPower, a YouTube filmmaking group, noticed his videos were disappearing from the browse pages - and he wasn't sure why. One of the group's successful tricks has been to use racy video titles and preview images to tempt viewers.
But a recent effort featured no worse than the group's leading lady, Tanya Derveaux, in a low-cut top. Even so, Mr Leysen said, the video quickly vanished from the most-viewed area despite having earned more views than many of the day's top videos.
A second iPower video was marked unsuitable for minors. This time it was Mr Derveaux in figure-hugging workout clothing.
YouTube's new policing highlights the tension between large and vibrant online communities and the businesses that own them.
That companies are charged with making judgments about political and artistic speech can be problematic, said Lawrence Lessig, a law professor at Stanford University and author of Remix, a new book that looks for a balance between art and commerce.
"I think it risks a significant animosity and scepticism," Mr Lessig said. "The whole excitement about the place is that we can see what the public is watching, what the public likes, what's important."
For its part, YouTube believes the stricter rules will boost the quality and relevance of the most visible videos by trimming undesirable clutter and less desirable material. "There's definitely this obligation we have to allow people to actually find what they're looking for," Mr Reyes said.
