Facebook’s acquisition of LiveRail closed today, a source told me, and Facebook confirms to me the deal is now official. Facebook announced the buy without disclosing a price back on July 6th, but multiple sources told TechCrunch the price was between $400 million and $500 million. Regulators apparently had no issue with Facebook buying LiveRail, which help brands that want to buy online video ads to target their spots and place them with publishers that have videos they want to monetize. The 170-person startup will start working with Facebook on Monday, a source said.

LiveRail could help Facebook better target the video ads it runs in the News Feed, and pipe in more advertisers. Meanwhile, Facebook could aid LiveRail with its own targeting of video ads across the web and mobile apps, plus connect it to Facebook’s vast array of ad clients. The close of the deal comes just days after Twitter launched its own video ad product, signaling there will be big competition between the social networks for ad dollars as they transfer from TV to digital.