Video-viewing site Hulu is experimenting with different business models and initiatives, from bumping up advertising to designing subscription-based content, to boost revenue, said NBC Universal's TV chief, Marc Graboff.

Hulu is helping increase viewing overall by drawing viewers to shows they may not have initially watched, but the challenge was in creating a model for Hulu that provides more revenue for its owners, said Graboff, chairman of NBC Entertainment and Universal Media Studios.

Hulu is jointly owned by General Electric Co's NBC Universal, News Corp's Fox Entertainment and Walt Disney Co's ABC.

Now the trick is ... to turn those digital pennies into digital dollars, Graboff said at the Digital Hollywood conference in Santa Monica. Hulu has got to bolster its economics.

I do think Hulu is experimenting with different models, he said. I know they're looking at any number of things, like adding inventory (more advertising) or creating a subscription model with different windows,

They'll eventually get it, Graboff added.

This week, Graboff said NBC's investment in popular video-viewing site Hulu was a step in the right direction but admitted its content owners may have been hasty in offering the programing for free on the popular video-viewing network to counter piracy.

Our research indicates that making shows available online has not cannibalized but has been additive, he said on Wednesday.

(Reporting by Sue Zeidler; Editing by Richard Chang)