That movie, with a budget of more than $1 million, had special effects (pirates materializing from the mist), and, yes, lots of sex. Two years later, the movie’s studio, Digital Playground, spent $8 million on a sequel  a remarkable sum in an industry where the average movie costs $25,000, according to the director of the two movies, Ali Joone.

But interest in DVDs has fallen sharply, Mr. Fishbein said, because the Internet has made it easy to watch snippets of video.

Mr. Fishbein estimated that pornographic DVD sales and rentals in the United States generated $3.62 billion in 2006 but had fallen as much as 50 percent since then. He says the slump has made some companies reluctant to share sales figures, so his estimates are getting rougher.

The big studios, like Vivid and Digital Playground, have turned to a subscription model, charging monthly fees for access to their Web sites and advertising the frequency with which they add new clips.

Mr. Joone said that of Digital Playground’s 60 productions this year, roughly 30 had little or no plot, up from about 10 two years ago. At Wicked Pictures, which averages one production a week, one-third are essentially just sex, twice as many as a few years ago, said the company’s president, Steve Orenstein.

“The feature is not as big a part of the industry today,” Mr. Orenstein said. But he says he still plans two to three bigger-budget releases each year, including the recently shot “2040,” which is about the pornography business of the future. Mr. Orenstein described the movie as “an almost Romeo-and-Juliet story between an aging porn star and a cyborg.”

In lieu of plot, there are themes. Among the new releases from New Sensations, a studio that makes 24 movies a month, is “Girls ’n Glasses,” made up of scenes of women having sex while wearing glasses.