When the fourth season of "The Office," an NBC comedy, had its premiere in September, one in five viewings was on a computer screen instead of a television. The episode attracted a broadcast audience of 9.7 million people, according to Nielsen Media Research. It was also streamed from the Web 2.7 million times in one week, the executive producer, Greg Daniels, said.

"The Office" is on the leading edge of a sharp shift in entertainment viewing that was thought to be years away: watching television episodes on a computer screen is now a common activity for millions of consumers.