The National performs at the Greek Theatre in Berkeley on July 29, 2016. Nick DeCicco/STAFF.

Director Tom Berninger did not gain an appreciation for indie rock after completing a documentary about his older brother’s Brooklyn band, The National. Mistaken For Strangers, which metamorphosed into a drama about the relationship of the two brothers, was clearly shot by an outsider to the scene.

That, the band’s baritone frontman said, is what made the movie better and different from other rock docs.

“He likes the band, but it’s not his music – he’s a metalhead, and he’s a horror movie fan,” Matt Berninger said a few weeks prior to The National’s performance at the Outside Lands Music and Arts Festival, while on tour in support of the band’s new album, Trouble Will Find Me.

“He wasn’t too enamored with our band or with any of us being rock personalities,” he said. “He wasn’t nerding out over the music. When he interviews the band members, he doesn’t ask hardly anything about the band because that was not something he was actually interested in. That’s how he made a much richer movie.”

While the brothers still disagree on music preference, they did stop trying to change each other and came to value their many differences.

“In a lot of the movie, I’m still trying to shape him and try to get him to get his shit together,” Matt Berninger said. “At some point, we both kind of had to understand to respect … that we’re just different types of people.”

And that’s part of the crux of the film, which premiered at the Tribeca Film Festival, and it may be the younger Berninger’s biggest accomplishment.

Nine years younger than the 42-year-old singer, Tom was living with his parents in Cincinnati when Matt got him a job as an assistant manager on The National’s 2010 tour to promote their fifth album, High Violet.

Matt is the only member of the Ohio-cum-Brooklyn quintet to not have a brother in the band – twins Aaron (guitar and keyboard) and Bryce Dessner (guitar), and Scott (bass) and Bryan Devendorf (drums) make up the rest of the brooding, melancholic quintet.

The singer wanted to reconnect with his brother and felt like he owed it to him to do so. The older brother went off to college when the younger was 9, and never returned home.

“I Should Live in Salt,” the opening track off the new album, is about the relationship between the pair and comes across as the older brother’s penance.

“He went through the whole teenage years with me being largely absent,” Berninger said. “So there was a part of me that wanted to reconnect with him. There was another part where he needed a job. He needed to get out of the rut that he was in.”

Tom Berninger had gone to film school and was most recently working odd jobs at a Cincinnati television station, where his life was stagnating, the older brother said.

“(We said) he could bring the camera along to make little goofy things that we would put on our website … and maybe make a video,” he said. “But that’s as much as we thought would happen from this stuff.”

While on the road with the National for eight months, the younger Berninger recorded 200 hours of intimate footage. But he made for an awful assistant manager, missing the band’s bus while partying, filming people he was told not to, and being overall a disorganized person.

Ultimately, the band’s longtime manager fired the assistant – a climax in the movie – and Tom ended up moving in with Matt and his wife. Matt was determined to not let his brother’s time with the band go to waste and prodded him to make something useful out of the footage he had shot.

Eventually, Matt’s wife came up with the idea of a gritty documentary about his time with the band, warts and all.

“It turned into a real movie about a significant thing, and it was not just a tour diary or a band profile,” he said. “It became a thing about him, and about relationships, and struggling to find your footing in life, and family.”

“I was blown away when I saw what was coming together with this thing,” Matt Berninger said. “It’s probably the most significant, important creative thing that I’ve been involved in.”

That speaks volumes coming from Berninger, who, like his band mates, is a perfectionist. The National has nearly broken up while recording previous albums, all in the name of creative excellence and the stress and anxiety that resulted from trying to achieve it.

That changed notably with the recording of Trouble Will Find Me, because the National expected to take a one- to two-year break following the previous tour and was not facing any pressure to create a follow-up.

“And so we really tricked ourselves into relaxing and not worrying about making a record,” he said. “That’s when, all of a sudden, the songs started just happening. That may have been one of the reasons why there was a casual, freewheeling vibe to how this record came about.

“Over the years, we learned to respect each other’s ideas and respect the process that the five of us goes through – meaning that it takes a while for us to bring ideas to fruition and meld them together into one thing,” he said. “We fought those fights and came through the other side. This time, we weren’t worried about the band dissolving, and we embraced the chemistry (and) process, and were at peace with it.”

Follow Roman Gokhman at Twitter.com/RomiTheWriter.