Hulu, the NBC Universal and News Corp. website offering video content, has sold out of its advertising inventory, according to NBC Universal President-CEO Jeff Zucker.

It is big news for the joint venture, which critics thought would be totally irrelevant upon its launch a few weeks ago.

More ad opportunities are on the way, Zucker said, but while internet video viewership is up, the money coming in is not replacing revenue earned from traditional 30-second TV spots.

"We are in a tremendous digital transition, the problem we face today is not that we don't want to make all of content digital -- we do -- but the economics are not there. We are cognizant that when content goes online, economics go down, but viewership goes up. The biggest concern is replacing analog dollars with digital pennies," Zucker said.

Although Hulu boss Jason Kilar said Hulu wasn't intended to be a YouTube killer, Zucker took a shot at the preeminent video website during a talk at the International Advertising Association's 41st annual World Congress in Washington on Monday.

"Advertisers want to be on something where you know what you get and not on something where you could be advertising [next to a video of] a cat on a skateboard," Zucker said.

Hulu streams clips and full episodes of current Fox and NBC shows like "The Simpsons" and "Saturday Night Live," classic shows like "Flipper" and "The A-Team" and movies like "The 40-Year-Old Virgin."

Zucker also revealed Hulu is in talks to add content from CBS, Disney and Viacom. He's also still hoping for an agreement with Apple's iTunes store that would set variable pricing on new episodes of TV shows, similar to what Apple currently does with movies.