<Warning: Slight spoilers ahead>

Scott Cooper is an actor’s director.

That term may be thrown around a lot, but the actor-turned-writer-director-producer truly fits the bill. After an “unremarkable career as an actor” (“I wasn’t going to have Matt’s career, Ben’s or Jude’s or all those one-named actors that we all know”), Cooper decided to follow in the footsteps of his favorite thesps, including his mentor Robert Duvall, who had all happened to have made that transition to the other side of the camera.

His background as an actor helped him draw out “realistic and truthful performances” from Christian Bale, Casey Affleck and Woody Harrelson, he told audiences following Nov. 25’s Variety Screening Series showing of his film “Out of the Furnace.”

“I think actors, when they are directed by actors — because we speak the same language — I think they feel safe, I think they feel like they can take risks, I think they feel like you’re going to have their best interest and protect them,” Cooper said.

This explains Cooper’s nontraditional approach to filmmaking. He shot his directorial debut, 2009’s “Crazy Heart,” in 24 days (“it almost killed Jeff Bridges”) and his latest drama in 33 days.

“One of the reasons that I shoot quickly, and it’s important to me, is I don’t tend to rehearse my actors,” he said during last night’s Q&A with Variety VP and executive editor Steven Gaydos. “Because if you do that, one, I think the performances become stale, and they feel like it’s movie writing, movie acting, movie talking. Secondly, it infuses the actors with electricity when they know that what you are rehearsing essentially is (what) you’re shooting.”

Instead of filming a performance, he wants to capture, almost voyeuristically, actions unfolding naturally in front of the camera.

“It’s really tough to capture performances that you feel like they aren’t performing, but that we’re spying on them,” he said.

He recalled one crucial scene between Bale and his love interest Zoe Saldana that was shot in three or four takes, but captured in the first.

“Christian remembers this differently,” Cooper said. “He thought that we did it over and over and over because he was just giving so much. It ultimately got to the point to where he just couldn’t give no more. … When you work with Christian Bale, you quickly realize that this is a very serious actor who gives 100% every take.”

Like Bale, Harrelson was completely immersed in his character, but much happier to leave his persona behind as soon as the film wrapped.

“His wife did not want him to play the part,” Cooper said. “She didn’t want to have to live with him in that space for two months. … He said, ‘I’ve never wanted to shed a character so quickly in my life.’”

Cooper shot the harrowing opening scene with Harrelson very last, when the actor had fully inhabited the character’s violent and misogynistic persona.

“I wanted the feeling of ‘Jaws,’” he said. “The way ‘Jaws’ opens so that kind of menace is established and every time we’re on screen, you know nothing good’s going to happen.”

While the opener was inspired by “Jaws,” the closer was a nod to “The Godfather: Part 2.”

“Typically, when you have an ending like that that’s ambiguous or doesn’t say anything, but hopefully will say a lot in time or if you’re at home and thinking about it 20 minutes after you’ve seen it or the next day. It’s also a bit of an homage to ‘The Godfather: (Part) 2’ where Francis Ford Coppola leaves Michael Corleone in his wingback chair as Fredo has just been murdered on Lake Tahoe and he too is living with the consequences of that violence for the rest of his life.”

That less-than-tidy ending was one of the factors that made the movie a tough sell to studios, but ultimately got made thanks to two big-name producers.

“It really takes a village to make any film, but to make a film like this, where most studios want to have nothing to do with a film like this, it takes Leonardo DiCaprio and it takes Ridley Scott,” he said.

The film, which has an almost autobiographical screenplay, was therefore a true passion project for Cooper.

“I sat down to that blinking cursor and I wrote it, essentially regurgitated a great deal of life experience and people that I knew and being the grandson of a coal miner, growing up in the shadow of the Appalachian mountains and having lost a sibling at an early age and all those sort of things that as Eddie Vedder said to me, ‘If you don’t write those down, they just eat you alive.’”