Mia Simonsen talks to a guest at the Rubicon Project booth during the Interactive Advertising Bureau (IAB) MIXX 2010 conference and expo during Advertising Week in New York, Sept. 27, 2010.

Public ad tech companies Telaria and Rubicon Project have agreed to merge as they try to make a stronger play in the growth of connected television and to bring an alternative to walled gardens like Google and Facebook.

Rubicon Project offers technology to automate buying and selling ads online, while Telaria is a software platform for managing video advertising. Rubicon Project stock was up nearly 5% at $7.56 per share in premarket trading Thursday. Its market capitalization is $383 million. Telaria's stock closed Wednesday's session at $7.52, down 3.2%, giving it a market cap of $350 million.

The companies said Thursday the merger makes it a major independent sell-side ad platform that will help it capture growth in connected TV. A statement from both companies said using Telaria's market position and tech expertise, the merger will bring the engineering and sales resources, broader geographic footprint and financial assets to "seize the CTV opportunity."

As an independent player, the companies said they create a "global, independent alternative to closed players in the ecosystem." As Facebook and Google undergo antitrust scrutiny, smaller players are trying to show the value and data they can provide outside the so-called walled gardens.

"Our businesses are highly complementary, and when combined, are a powerful, strategic alternative to the walled gardens, which have been frustrating both buyers and sellers due to their lack of transparency, innovation bottlenecks, and conflicted business models," Telaria CEO Mark Zagorski said in a statement.

The stock-for-stock merger has an exchange ratio of 1.082 shares in Rubicon Project common stock for each share of Telaria common stock. Telaria stockholders are expected to own about 47.1% of the combined company, while Rubicon Project stockholders are expected to own about 52.9% of the fully diluted shares of the combined company.

Current Rubicon Project President and CEO Michael Barrett will serve as CEO of the combined companies. Zagorski will be president and chief operating officer of the combined companies. Rubicon Project Chief Financial Officer David Day will retain the role within the combined company.

The companies said over the 12 months that ended Sept. 30, Telaria and Rubicon Project's aggregate revenue was $217 million, a 32% year-over-year increase.

The transaction is expected to close by July. The companies said they had not yet decided what the combined name would be.