comScore just completed the stock swap acquisition of Rentrak it announced in September, creating a digital and TV audience measurement power that could give Nielsen pause.

The combination of comScore’s digital media data with Rentrak’s TV information from set top boxes and movie theaters should make it useful to networks and advertisers that want more insight into audience behavior. The company says that it will measure more than  260 million desktop screens, 160 million mobile phone screens, 95 million tablet screens, 40 million television screens, 120 million video-on-demand screens, and 40,000 movie theater screens.

“This proven ability to precisely measure extremely fragmented, dynamic audiences in dramatic, innovative ways — and to quickly report on it — has provided the insights that allow our clients to act with great competitive advantages,” comScore CEO Serge Matta says.

In an apparent swipe at Nielsen’s surveys, comScore President Bill Livek says that media “can no longer be measured with samples in the thousands of households or individuals. The solutions our customers need must be based on unifying and making actionable massive amounts of information they can use as both a currency and to better manage their businesses. Our joint cultures have been living and breathing this mission from our companies’ inceptions.”

But some analysts expect comScore to complement Nielsen’s data, not replace it.

comScore and Rentrak together generated $500 million in revenue last year, which leaves the combined company “materially smaller than Nielsen,” which made $2.8 billion from audience measurement, Macquarie Research’s Tim Nollen says.

What’s more, he says, “Nielsen is the standard for TV ratings in the US, which gives it an almost unassailable position in this core business. comScore/Rentrak will have to position itself as an alternative data services provider to penetrate client research budgets.”

comScore’s role in the market is also complciated by the fact that ad giant WPP owns about 18% of the company.