Yesterday's news that Nielsen is collaborating with GroupM, the largest media buyer in the world, to introduce "Nielsen Cross-Platform Campaign Ratings," is the latest move by the Nielsen to get its arms around the elusive problem of coherently measuring online video advertising. As I recently wrote, many in the advertising and content community believe there's a "measurement crisis" as video consumption rapidly splinters to numerous new connected devices.

Given that "what can't be measured, can't be sold," cohesive online video measurement is essential. And since Nielsen is the gold standard in TV ratings, many in the industry have expected it to pick up the mantle in online video as well. That has led to some grumbling at Nielsen's perceived slow pace of innovation, and the drag this creates on online video ad spending.

There do seem to be signs of progress. Last September, Nielsen announced that it had received MRC accreditation for its Nielsen Online Campaign Ratings (NOCR) measurement system that attempts to provide the equivalent of a Gross Rating Point (GRP) for display and online video advertising. Of course, some in the industry reject the notion that online video advertising should embrace TV's GRP approach, as it doesn't fully capture key new engagement attributes. Nevertheless, in February, Unilever became the first major advertiser to adopt NOCR for all of its brands' digital campaigns. As Unilever shares its experience, other advertisers are likely to follow this year.

Nielsen also seems to be integrating itself more deeply into the online video advertising industry. Last December, it announced an alliance with Tremor Video's VideoHub division allowing clients to access NOCR GRPs to help understand what demographics their ads reach as well as viewer engagement with particular ads. Separate, there are also Nielsen tests underway with cable operators to understand viewership in their iPad apps. As this initiative develops further, it could be a critical input to helping accelerate TV Everywhere rollouts.

Measure of online video is complicated though, and seems to only get more so each day. For example, Apple's disclosure yesterday that it has already sold 3 million new iPads suggests that hard-to-measure in-app video viewership could soon soar as content providers are drawn to the huge iPad audience and the new device's higher-quality screen.

Add it all up and it's clear how difficult accurately measuring video usage is going to be in the connected device era. Nielsen is moving along, but device-makers, content providers and viewers aren't slowing down to allow it to catch up.