Nielsen is taking a big step in measuring streaming TV today with the addition of Hulu and YouTube TV to its ratings.

Nielsen’s President of Product Leadership Megan Clarken said that the company’s ratings (the best-known measurement of TV viewership) have included some streaming data before, but it was usually when “traditional networks … distributed their content onto digital platforms” — like when CBS launched its streaming service CBS All Access.

“This is the first time the biggest digital-first, TV streaming companies have come into the fold in terms of being included in TV ratings,” Clarken said.

She added that this move reflects how viewership has moved beyond the traditional “TV glass.” It also comes just a few months after Hulu and YouTube launched their live TV services.

More specifically, Clarken said data about Hulu and YouTube TV will be incorporated into Nielsen’s C3/C7 numbers, which are used by TV ad-buyers and reflect viewership during a three- and seven-day time window.

And while Nielsen’s traditional method for determining ratings is based on a limited number of representative “Nielsen families,” Clarken noted that the firm’s “digital in TV” numbers are calculated differently: Streaming services actually include the Nielsen SDK in their video player, allowing for direct measurement of viewership.

Device IDs (in encrypted form) are then synced up with Facebook data to determine the demographics of each viewer. There is, however, still a panel involved in the process, since some viewers, such as younger children, aren’t on Facebook.

Will Nielsen be measuring other streaming services in the future? Clarken said she can’t make any predictions, but it’s certainly possible: “The doors are open for those players who want to be lined up side-by-side and measured in a comparable way to traditional TV.”