Measuring online video ad engagement is a notoriously tricky process: Traditional performance metrics are flawed as a result of standard use-cases which affect measurement and attribution. Those include consumers using multiple browsers and devices to access the Internet; users accessing brands via both Web sites as well as apps; certain web browsers as well as iPhones and iPads not accepting third-party cookies; and security programs, which tend to delete third-party cookies on average every seven days.

Google hasn’t made things easier for YouTube advertisers, either, because it has always blocked the ability for Nielsen, comScore and other established ratings companies to place measurement tags on ads running on the site. Those allow marketers to monitor the performance of online ads by tracking the number of people who see the ads, how long they watch them, and how often. Google has wanted brands to use its own in-house measurement service to track this—a state of affairs that has met with lukewarm support from advertisers. So, the search giant—which makes its living on eyeballs—has decided to relent, and is opening the kimono to third-party tracking.

Nielsen’s tags will be accepted across all Google properties, including YouTube, by early 2014.

“We know our clients want meaningful measurement, which is why we’re investing in brand-friendly metrics,” Google said in a statement. “While we continue to build measurement options powered by Google, we’re also partnering with industry leaders, such as Nielsen and comScore, to offer objective, credentialed, third-party measurement options.”

The move is also motivated by the fact that Google is feeling some, “show me the money” heat from its professional content producers. Online video advertising spending is expected to top $4.8 billion this year, but YouTube’s rates have been falling.

 “YouTube has literally DESTROYED – with a capital DESTROYED – the video ad market,” said Andrew Baron, creator of the video aggregator site Magma, writing in Tubefilter. “What started out as a standard and relatively reasonable benchmark of $25 CPM for both broadcast sales and online video sales just a few years ago, is now down now to around a $2 take home this year.”

If it can increase measurement accuracy and allow advertisers to wrap YouTube into a larger media buy, YouTube could start to command better rates, setting itself up for a different kind of business modeling going forward.

To that end, Nielsen, which is the largest and in many ways most-trusted measurement outfit in the business, will now be able to provide demographic data about who sees the ads within the context of holistic campaigns, such as television, other digital properties and mobile, all of which it also tracks. Advertisers then get a better view of brand engagement in a multiscreen world, and can negotiate ad buys across properties.

The move is of its time, as digital video advertising and measurement matures. "The inaccuracy of current measurement models is an alarming industry trend and more specifically, extremely problematic for digital marketers," said Thatcher Clay, vice president of data research for Trueffect, which recently launched its Trupath audience-based measurement platform. "In a market where the growth of the industry is evaluated on effective measurement of both campaign and performance… advertisers and agencies [need] improved confidence in where to most effectively invest their media dollars."