David Ayer had "nowhere to hide" on the set of Heart of the Beast.

The 58-year-old director has helmed the new movie, which sees Brad Pitt's retired Special Forces veteran James Belmont and his dog Odin trying to survive in the Alaskan wilderness following a plane crash, and confessed that the "simplicity" of the premise increased the complexity of the production.

Speaking to IndieWire's Filmmaker Toolkit podcast, Ayer said: "It was a bigger challenge than I understood going into it. I really didn't know what I was in for.

"The simplicity of it exposes the filmmaking in ways I never imagined. Your decisions, tone, mood, and performance count more than ever in that situation. There was nowhere to hide."

Ayer explained how he opted to direct the movie after Cameron Alexander's script provoked strong emotions.

The Beekeeper helmer said: "I think it triggered part of my own grief over the loss of my father when I was young, and this sort of aspirational desire in me.

"I wish I had someone who looked after me the way James looked after Odin. I wish I had that kind of unconditional love and support."

Ayer also hailed Pitt for taking a part that wasn't "traditionally engineered as a movie star role".

He said: "I think it has to do with his willingness to jump into material that isn't so traditionally engineered as a movie star role, or traditionally masculine.

"He's open to the deconstruction. And he has a lot of range, and I feel like he doesn't always have the opportunity to find those dichotomies in himself.

"Maybe there's also a kinship there in our understanding of traditional masculinity, the masks men are given in life to wear, and the fact that there's often a confused beating heart beneath them."

Ayer says that Heart of the Beast was made even more challenging by the compressed production schedule.

He explained: "It was a whirlwind, so it really put Brad on the spot as an actor, and me on the spot as a director.

"I had an amazing production designer, Greg Berry, and we came up with this visual journey that reflected the inner journey of the character.

"Brad's very internal, so much of our work came in prep, mapping out the emotional beats and the tone. And then once he gets to set he will grind and exhaust himself."

Ayer felt that Pitt's vast acting experience was pivotal during the making of the movie, particularly because he did much of his work alone.

He said: "Normally on a set, you have the director's chains lined up, and the actors sit in them and socialise.

"He had nowhere to go other than to be cold and tired and emotionally exhausted by himself. They say acting is reacting, and he didn't have a big cast to react to and pass the energy back and forth - he had to react to the circumstances.

"He's not getting any of the normal support an actor would in a scene. It was like a jet pilot flying a solo mission."

Ayer added: "All of the details come from a lifetime of experience.

"Brad's done an amazing amount of movies and was in a place where he was willing to be vulnerable in ways he hasn't before.

"I've done a few movies and feel like I'm just beginning to come into my own, and I was open to really challenge myself both emotionally and as a filmmaker. So everything came together."