Google has revealed its InVideo advertising program on YouTube - a new way for companies to reach the video sharing site's 130 million viewers.

Advertiser's clips will now appear on select YouTube videos, not as a "pre-roll" but as "overlays" which apparently look will be as scrolling messages that run at the bottom of the screen.

Fifteen seconds into a video with an overlay, viewers will be "invited" to view the ad and if they want to the clip is paused and the ad is shown in a flash player in the video window.

If users choose not to click to watch the advert, it disappears after 10 seconds, and will not reappear if the video is replayed.

Trial advertisers include big names like 20th Century Fox, Warner Music and BMW.

"We're not going to put ads on every user-generated clip," says Eileen Naughton, Google's director of media platforms.

To in the ad scheme, users must "have a following" on YouTube. "We're looking at a mix of professional sites and originally created content", she says.

It has massive potential for advertisers getting exposure across the internet, and for Google to make money on its billion dollar investment in YouTube, but analysts say it will take time for the scheme to kick in and add cold hard cash to Google's bottom line.