LOS ANGELES - The new film "Mistaken for Strangers" featuring The National certainly has a lot of the band in it. But it's not about The National. It's much more about singer Matt Berninger and his brother Tom, and the measure of success, particularly among siblings.

The National is made up of Berninger plus two pairs of brothers, with Bryce and Aaron Dessner, and Scott and Bryan Devendorf. When Matt invited his brother Tom to become a roadie on The National's frequently sold-out world tour a couple years ago, "I wanted him to bring his camera to maybe make some videos or stuff for our website. He didn't even know he was gonna be making a feature film at that point," Matt told me in our HitFix interview. 

No, "Mistaken for Strangers" did not turn out to be "a slick, cool profile" but a summary of Tom's struggle with feeling aimless and struggling with his own self-identity next to his successful indie-rock brother. It was a question of "at what point did I go down the wrong path," Tom explained in his own words, "a look into who I've become, and who I have become is not so bad, and I just had to roll with it."

That "look" included some cringe- and tears-inducing moments -- for the brothers as well as for the audience. Interviews with the Berningers' parents; footage of Tom getting fired from the tour;  Matt's frustrations with his brother; heady moments from the stage and behind it all took place just prior to and during the recording of the band's 2013 album "Trouble Will Find Me."

"When I was finishing the movie on his band, I realized a better movie was not having the band in it that much," Tom explained about this "soul searching." After the film debuted at the Tribeca Film Festival last year, he got feedback that he wasn't alone in this family or creative dynamic.

For the The National, they too have had periods of drought that made them ask serious questions about "rolling with it."

"We got knocked down a bunch at the beginning," Berninger said, after explaining what he meant in "Strangers" by saying his band's had "good luck."  "We kept clinging to the positive things. You can let bad luck stop you, or you can just ignore it," advising that when only two people showed up to the shows, to play your heart out to them. "There days when there were none..."

Those sparse gigging days seem to be gone. The band has release six full-lengths, gone on a number of successful tours and diversified by sometimes working on solo projects, film scores, soundtrack spots and, well, have become a "Bob's Burgers" holiday staple. The last three full-lengths have all been released in May, three years apart, but Matt said he wouldn't be surprised if the follow-up to "High Violet" may take a little longer.

Watch the full interview with Matt and Tom Berninger above to learn more about The National's recording process and what the band didn't want out of Tom's documentary.

"Mistaken for Strangers" heads to theaters, VOD and iTunes tomorrow (March 28).