Sometime in the next few weeks, visitors to Hulu, the online video site jointly owned by NBC Universal and News Corp, will be able to do something that television viewers would never have imagined just a few years ago: choose their own advertising.

When, for example, an advertisement sponsored by a carmaker pops up, viewers might be asked to click on a sports car, a pick-up truck or a family sedan, depending on their preference, and watch a corresponding message. (Skipping past, unfortunately, is not an option.)