Facebook will begin selling 15-second video ads later this week. Since September, Facebook has been testing a way to make videos more engaging on Facebook. Now the company is beginning to test a similar video viewing format for advertisers. Marketers will be able to use this new format to tell their stories to a large number of people on Facebook in a short amount of time.

Starting from this week, a small number of people will see video ads for the new film 'Divergent' begin playing as they come into view in News Feed on mobile and desktop.

Rather than having to click or tap to play, videos will begin to play automatically as they appear onscreen - without sound - similar to how they behave when shared by friends or verified Pages. If the video is clicked or tapped and played in full screen, the sound for that video will play as well. At the end of the video, two additional videos will appear, Facebook said. If you don't want to watch, you can keep scrolling and the video will stop playing.

On mobile devices, all videos that begin playing as they appear on the screen will have been downloaded in advance when the device was connected to WiFi - meaning this content will not consume data plans, even if you're not connected to WiFi at the time of playback.

Facebook's move would follow efforts by Facebook?s online rivals to capture ad dollars that have traditionally gone to TV networks. Google began funding original content channels on its YouTube video-sharing site in recent years, giving it a more curated venue for commercials.

Facebook?s move also would step up competition with social-networking rival Twitter , which has been courting TV advertisers in its bid to reach $1 billion in sales by 2014.