For his 20th feature film, “The Girlfriend Experience,” director Steven Soderbergh has returned to a theme he explored in his breakthrough “sex, lies and videotape”: infidelity. Yet the Oscar-winning director of “Traffic” and blockbusters such as “Ocean’s Eleven” refuses to play it safe. Like his recent projects “Bubble” and “Che,” “The Girlfriend Experience” is available for PC download and pay-per-view simultaneous with the theatrical release. And Soderbergh crossed an invisible line when he cast adult-film star Sasha Grey in the lead role.

I spoke by phone with Steven Soderbergh last week.

Q: Did the original idea for this movie come from you or from the screenwriters (Brian Koppelman and David Levien, who wrote “Ocean’s Thirteen”)?

A: It landed on us at the same time. We were together at a bar in midtown Manhattan when I saw a woman who seemed disconnected from everything else that was going on there. I asked them if they could figure out how she fit in, and they both said “Oh, that’s a G.F.E.” And they started explaining that there is a whole tier of high-end escorts who provide what’s called the girlfriend experience. Customers pay for an extra level of intimacy where they make out with you and they learn about your life and become like your girlfriend for the hours that you have them. And I immediately thought that would be a good idea for an HD movie.

Q: In your subsequent research, talking to escorts, did you find that this is particular to New York or is it a global phenomenon?

A: If you’ve stayed at a nice hotel anywhere in the world for more than 20 minutes, you’ve seen hookers. But because of the cost per hour, the GFE happens where there’s an extra amount of money flowing around—New York, L.A., London, Sydney. Madrid, Tokyo, Hong Kong. We set the story in New York because I wanted to shoot a movie where I live.

Q: In the movie, both Chelsea and her boyfriend Chris are always on the make, looking for opportunities to close a deal. Is that your sense of the wider America, circa November 2008, or is this movie about a particular class?

A: To me, it doesn’t represent America or even the whole of New York. It’s about a very specific strata of this city at this time. I wanted it to be myopic. But I do think you can extrapolate and ask yourself, to what extent are we all weighing our lives in terms of transactions, whether emotional or material?

Q: How many of the people in the movie were non-actors who were simply speaking and behaving like they normally would?

A: All of them! Sasha is the only person who had ever been in front of a camera before.

Q: Were many of the scenes improvised?

A: The script was a general outline that said what the goal of each scene was: who’s trying to get what. But we cast people who were very similar to what they play in the movie, so you’re just winding them up and letting them go. In the case of Chris, he really is a personal trainer, and for the scene where he’s trying to sell the customer some extra sessions, I just pulled Chris aside and told him not to take no for an answer. And for his customer, who really is a Wall Street guy who works with a trainer, I told him not to say yes under any circumstances.

Q: When you’re working with non-actors, how many takes take do you generally have to do?

A: As it turns out, the fewer takes the better. Once you get beyond one or two takes, they start performing, and you don’t want that. As a director, you have to let go of trying to control it and just deal with what they do. To relax them I would say, there’s no wrong answer. Just be yourself, and I’ll figure out how to turn it into a movie.

Q: When Jason Reitman was in town filming “Up in the Air,” Paramount told him he could watch any movie in the studio’s library to get inspiration, whethe rit was “Harold and Maude or “The Godfather.” Before you shot this movie, did you study films about prostitution, like “Klute” or “Crimes of Passion”?

A: In this case, I was watching Godard. Fassbinder’s always good, Antonioni’s always good. I was looking for a way of revealing info and composing scenes. For every movie, I assemble a tool kit, and for this one, it was mostly European films of the ’60s and ’70s. I wanted it to be like a documentary in which things are happening spontaneously, but I also wanted it to be very constructed and stylized. For some people, those might seem like antithetical ideals, but I wanted to fuse them.

Q: Because so many of the characters are rich people fretting about money, do you feel that this movie documents a moment in history when everything changed?

A: We were very lucky to be shooting right before the election, because there was so much going on, and I think the specificity works to its benefit. But it would have been a mistake if the narrative had relied on those events. The fact that there’s an election is just sauce that gives the film flavor.

Q: But do you foresee a change in the kinds of films that will get made in the Obama years?

A: I think for a few years we will veer away from political cynicism. I have friends who had political movies in the pipeline that took a jaundiced view of the world, and those movies have been tabled while we play out the new optimism. Right now I’d be hard-pressed to make a serious movie about the problems of the super rich, but it would be a blast to make a dark comedy about it.

Q: You’re rumored to have at least five other movies coming out. What’s next?

A: I’ve got a movie about Spalding Gray that I hope we’ll finish editing by the fall. “Moneyball,” based on the book about baseball executives, we’ll be shooting this summer. The Cleopatra project (a ’20s musical featuring Catherine Zeta-Jones and a soundtrack by Guided By Voices) will shoot next year, and so will the movie about Liberace (starring Michael Douglas).

Q: And in the fall you’re releasing “The Informant,” the thriller with Matt Damon that you partly filmed at the St. Louis airport last year. How can you work on so many projects at once?

A: I work with the same team all the time, so as we’re finishing one project, we’re able to start prepping for the next. I set things in motion, then before I get bored, I move on to something else. It’s a bit like plate spinning. Or infidelity.

The “Girlfriend Experience” opens at the Tivoli on Friday, May 22.