Facebook is expanding the availability of 15-second video ads to “a select group of advertisers,” the social giant announced.

Facebook didn’t reveal which new advertisers it’s working with on Premium Video Ads, nor would it disclose ad rates. The company said users will begin seeing the new ads over the next few months.

The social media company, which currently boasts 147 million daily active U.S. users, kicked off a test of the video ads in December with Lionsgate’s Summit Entertainment. The studio launched a series of video ads for “Divergent,” the sci-fi pic starring Shailene Woodley, Kate Winslet and Theo James that opens nationwide on March 21. Watch a demo of the “Divergent” ad on Facebook here.

SEE ALSO: Facebook Launches Video-Ad Test with ‘Divergent’ Teasers from Lionsgate’s Summit

The video ads automatically start playing “in-line” in a user’s Facebook feed, with the audio muted by default. If the video is clicked or tapped and played in full screen, the sound for that video will play as well.

According to Facebook, Premium Video Ads are bought and measured in a way that’s similar to TV advertising. The company is selling inventory based on targeted gross rating points (GRPs) to reach a specific audience over a short period of time. Delivery is measured by Nielsen’s Online Campaign Ratings (OCR) service, and advertisers only pay based on the impressions OCR measures.

The company claims it can predict and deliver with 99% accuracy a campaign’s total audience reach and the amount of times an ad was seen. Advertisers also have the ability to buy video ads by daypart (like TV), choosing specific time periods when ads run.

Facebook is working with analytics provider Ace Metrix to review and assess “how engaging the creative is for each ad — before it appears on Facebook,” product marketing manager Susan Buckner wrote in a blog post. Under the partnership, Ace Metrix will give Facebook an objective measure to analyze such factors as “watchability,” meaningfulness and emotional resonance.

According to Facebook, on mobile devices, video ads will be downloaded only over Wi-Fi connections, meaning they won’t eat up bandwidth that counts toward a monthly wireless data plan.