Yahoo CEO Marissa Mayer plans to transition her Web portal into a video hub and she took a giant step to making that happen by acquiring video advertising company BrightRoll, reports Fortune.

According to Businesswire, Yahoo announced Tuesday that it's buying San Francisco-based BrightRoll for $640 million in cash.

BrightRoll, founded in 2006, is expected to generate more than $100 million in revenue this year, according to Yahoo. The multinational Internet corporation said it will add BrightRoll's 400 employees to its digital advertising team.

"This acquisition will accelerate the growth of both companies -- we can help BrightRoll scale to even more advertisers globally, and they can bring their tremendous platform offering to Yahoo's advertisers," Mayer said in a statement.

In a newly published blog post, Mayer said that video is one of Yahoo's main growth areas and that the acquisition will help their video ad platform become "the largest in the U.S." She also revealed that BrightRoll receives 2 billion ad requests daily and should produce $100 million in net revenue this year, making it very profitable.

Mayer wrote that internet video advertising is increasingly fragmented across thousands of sites and mobile apps, adding:

BrightRoll provides an effective solution aggregating high-quality publishers together into a unified network and utilizing programmatic advertising to allow real-time buying on the largest set of online video advertising inventory available. BrightRoll's approach not only benefits advertisers and publishers, but also improves experiences for consumers, through better quality, more relevant advertisements.

Activist investor Starboard Value criticized Mayer's acquisition strategy claiming none of her acquisitions have been fruitful. Mayer countered by pointing out the $1.1 billion Tumblr purchase -- her largest acquisition -- added users and is a source of revenue growth this year, according to Fortune.

Yahoo is expected to complete the BrightRoll acquisition in the first quarter of 2015.