YouTube’s viewing growth — via Nielsen data — continues to show big double-digit percentage gains — although it is decelerating slightly.

Looking at Nielsen’s Digital Content Ratings for March, Pivotal Research Group says viewing was 27% higher in March — 6 billion to 7 billion person-viewing hours per month. That’s down from 30% gains in previous periods.

This compares to traditional TV ad-supportable content — excluding video-game consoles, DVDs, SVOD, premium / pay TV, etc. — of around 30 billion person-viewing hours per month.

But monetization when comparing TV to YouTube is far different, says Brian Wieser, senior research analyst at Pivotal: “Only a minority of YouTube’s content is of comparable quality to advertisers.”

Although U.S. YouTube consumption equates to around 15% of global YouTube activity, Wieser says: “The U.S. probably accounts for around half of the service’s global revenue, which, in turn, is probably around half of the world’s digital video ad spending outside of China.”

Pivotal says 82 media brands total 50% of all YouTube consumption — mostly music-related brands.

In March, Broadband TV had a 4.5% viewing share of YouTube total viewing; UMG (Universal Music Group), a 3.4% share; Vevo (its owners include Vivendi’s UMG, Sony and Warner Music), 3.3%; Warner Music: 3%; Studio71, 3.3%; FullScreen (owned by Chernin Group and AT&T), 3.0%; SonyBMG, 2.3%;

Those under 2% include The Orchard (owned by Sony), 1.8%; Disney/Maker Studios: 1.5%; Machinima (owned by Time Warner), 1.2%; StyleHaul (primarily owned by RTL), 1.2%; Curse Entertainment, 1.0%; and CollabDRM, 1.0%.