Mark Duplass took everything he learned in film school and poured it into his art. Except Duplass’ art, by his own admission, wasn’t very good.

Duplass and his filmmaking brother Jay came to that awful realization during their mid-20s, a time when many of their peers were finding their way as hedge fund managers and other successful pursuits.

So the Duplass brothers went back to basics.

“I said to Jay, ‘we’re gonna make a movie today like we made movies when we were 5 and 8 years old – no lights, no sound gear, no propriety, no bullshit. Just two little doofus kids trying to make a movie,'” he recalls.

The result, a short film about a man trying to perfect his phone answering machine message, was “one of the ugliest and worst sounding movies you’ll ever see. But it was our first movie to get into Sundance,” he says. “It taught us when we access that comedy and humanity and darkness in ourselves, even if it’s hi-fi or low-fi, people connect with it.”

“Film school can be really healthy for people, but it wasn’t super healthy for us,” he says. “It took us away from where our instincts were.”

The brothers Duplass had found their voice, ironic for a duo who would become known for leading the so-called Mumblecore indie movement with films like “The Puffy Chair” and “Baghead.”

Duplass visited the just-wrapped Starz Denver Film Festival last week to screen his Paramount comedy “Jeff, Who Lives at Home.” It’s the writing/directing team’s second “major” film, coming on the heels of last year’s “Cyrus” starring John C. Reilly, Jonah Hill and Marisa Tomei.

“Jeff,” which hits theaters in Spring 2012, stars Jason Segel as a slacker who thinks life has something special waiting for him. So he puts off getting a job, a girlfriend or an apartment until he sees a sign as to what that might be. “The Hangover’s” Ed Helms co-stars as Segel’s slightly more composed brother, while Judy Greer plays Helms’ wife who may be having an affair.

Susan Sarandon, known more for her dramatic chops, steals a scene or two as a lonely 60-something who finds romance in an unusual fashion.

Duplass figured Sarandon might come on the set with an attitude given her stature and film experience. Heck, he wouldn’t blame her given her impressive film resume. Instead, the Oscar winner appeared giddy to try the brothers’ patented style of improv filmmaking.

“I haven’t done this a lot before, I hope I’m good at it,” he recalls her saying. “It took a lot of trust on her part … people throw that word around a lot, but it’s a big deal for an actor of her experience to trust younger directors doing something completely new.”

“Jeff” should make audiences laugh, but it’s a complicated comedy that deals with shattered expectations, marital distress and the notion that family ties can strangle as well as bind. Duplass had no concerns about casting Segel, known for his comedic turns in “Forgetting Sarah Marshall” and CBS’s “How I Met Your Mother,” to corral those darker moments.

“It’s a similar process with Jonah Hill in ‘Cyrus,'” he says. “He’s a funny, funny dude … and then you meet with him and there’s so much more going on.”

Segel’s versatility matters. “Jeff” isn’t a cookie cutter comedy, or one brimming with gross-out gags or goofy cameos.

“The script is one click off from what Paramount would normally require for a big comedy,” he says. “Our pacing is not perfect, choppy-choppy jokey-jokey. We do a lot of dramatic stuff in there. It’s got rough edges to it. It has a non-cynical feel to it that will allow us to connect [with audiences].”

Good thing the film’s came in at about $10 million, minus some tax breaks given by Duplass’ home state of Louisiana where the film was shot.

“Jay and I, in general, are believers in being fiscally responsible in the age of endangered independent film,” says Duplass, who also acts in indie movies as well as the FX series “The League.” “We hear so many directors complain that they can’t get more money for their weird little movie. If you’re making a movie about two lesbian sisters who decide to have an affair and get murdered in Rwanda, that movie should be made for $500,000. It’s not a big movie, so don’t be upset when you’re not getting your $10 million to make that movie.”

That’s pretty straight talk from a man who starred in “Humpday,” the 2009 tale of two straight pals who accept a dare to have sex with each other. But for Duplass, the movie business has been all business for some time now.

“We were doing pretty intense drugs at 12-13, and drinking a lot by 14,” he recalls. “At 16 I thought, ‘I’m done with that. I’m ready to start our career.’ We were very serious as artists from a young age.”