BusinessWeek reports that the current test is confined to sites that are part of Google's AdSense network, but that, if all goes well, the company could expand the system out to other video providers.

How much will Google's effort change the way we're fed ad messages online? The answer depends on which publishers take advantage of the service. Google would not say whether the AdSense partners involved in the trial are major media companies or primarily smaller Web publishers.

Large media companies, of course, are no strangers to in-stream ads. Often, they insert unskippable commercials in online broadcasts of their shows and, in some cases, before videos themselves. And since users are accustomed to watching commercials on televised shows like ABC's Lost, why not sit through an ad inserted into the online version?

Google has said that the ads, which will be no longer than 30 seconds, can be made skippable for users. Wired's Adario Strange writes that the new ads could potentially be a big deal for smaller advertisers.

The door this Google announcement opens up is huge. Small advertisers will now be able to broadcast (online) television commercials on the cheap, and the thousands of indie videographers out there playing with YouTube will finally have a target market for their underused services. On the other side of the coin, video bloggers (independent and big business-backed) will soon have a clear cut way to monetize their efforts beyond piece meal blog network ads and spotty sponsorships. Did I mention this is a very big deal?