A technology designed to detect copyright material could give YouTube a needed dose of legal legitimacy and calm any concerns Google Inc. (GOOG) has about spending $1.65 billion on the Internet video site.

But that same technology could hurt YouTube's edgy appeal.

While YouTube is known as the place to find almost any kind of video clip, recent agreements with high-profile content creators require YouTube to deploy an audio-signature technology that can spot a low-quality copy of a licensed music video or other content.

YouTube would have to substitute an approved version of the clip or take the material down automatically.

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Analysts said that stepped-up monitoring by entertainment companies raises the likelihood that YouTube fans won't find what they're used to getting — and will go searching for the next online video rebel.

"There's very little that holds YouTube's audience to YouTube except the belief that whatever they want to see, there is a very good chance YouTube will have it," said Joe Laszlo, senior analyst with Jupiter Research.

"If the video migrates to other places, I fear the audience will too, so YouTube needs to be really careful about how it does this," he said.

YouTube offers a gold mine of clips depicting all manner of amateur hijinks and tons of unauthorized commercial videos. Kevin Davis, a 16-year-old from Torrance, Calif., likes to peruse YouTube for music videos by R&B singer Chris Brown and rappers Lil Wayne and The Game.

"I find what I'm looking for most of the time," he said.

YouTube, based in San Mateo, Calif., has licensing deals with CBS Corp. (CBS) and three major recording companies — Warner Music Group (WMG), Vivendi's Universal Music Group and Sony BMG Music Entertainment.

The entertainment companies will get a cut of YouTube ad revenue each time someone views a video licensed by them.

YouTube stressed that it won't be filtering content itself.

Instead, the technology it's developing will allow copyright owners "to identify their content, locate it and then make a decision based on whether they want to remove it," said spokeswoman Julie Supan.

The new technology will be designed to scan a digital audio file, such as an MP3 or video, and compare the electronic "fingerprints" to databases of copyright material.

But copyrights can be tricky on sites like YouTube. Even a homemade video can run afoul of the law if it has a professional song playing in the background. Amateur concert footage and other video may be pulled from sites as a precaution simply because it's unclear who owns the rights.

"We're going to probably see a lot of instances like that," said Michael McGuire, a technology analyst for Gartner Inc. (IT) "It's going to be a constant game of cat and mouse."

YouTube did not provide further details on the technology, which it expects to roll out by the end of the year.

Some analysts doubt the screening technology will be foolproof.

For example, detecting someone singing a copyright song on a homemade video could be difficult because the sound would not exactly match the original recording.

"It's impossible to be completely effective," said Josh Bernoff, a digital video analyst with Forrester Research. "The devil's in the details."

YouTube's final product could resemble a system developed by Audible Magic Inc., which has compiled electronic fingerprints for more than 4 million recordings to compare to content posted on iMesh, an online file-sharing application.

Another video-sharing site, Guba LLC, which hosts user-generated videos as well as Hollywood movies that can be streamed or downloaded for a fee, uses a different content filtering technology dubbed "Johnny" that has been endorsed by major film studios.

The application tracks the transition of images in a video, like a series of snapshots, to build a signature used as a basis for comparison.

Banned content can be matched against Guba's video database and flagged, regardless of whether its format, resolution or file size are different than the original, said Bart Myers, Guba's senior vice president of product development.

"The beauty of Johnny is that Johnny doesn't care," he said.

The company claims the technology is more than 90 percent accurate with video clips that exceed three minutes. But the shorter the clip, the harder it is to spot a match.

Some sites such as Microsoft Corp.'s video-sharing hub Soapbox don't use any technology to filter what gets uploaded. But that appears to be changing.

In a statement, Rob Bennett, general manager of MSN's entertainment and video services unit, said the company is developing technologies to protect content owners.

Other sites fgure to follow.

"We expect that all of our partners in this space are going to implement state-of-the-art content-filtering technology," said Michael Nash, a senior vice president at Warner Music Group.