Those expecting a traditional rock documentary on The National, mapping the heralded Brooklyn indie rock band’s trajectory from its shaky origins in 1999 to its gradual breakthrough as rock stars, will be sorely disappointed by “Mistaken for Strangers,” directed by National frontman Matt Berninger’s nine-years-younger brother, Tom Berninger. The film opened the Tribeca Film Festival on Wednesday night.

Not that there isn’t plenty of live footage from the band’s 2010 European and US tour–supporting the album “High Violet,” which many say catapulted The National into the mainstream–and scattered interviews with individual band members. But “Mistaken for Strangers,” while certainly up-close-and-personal, is too erratic and self-conscious to simply zero in on the band. It’s similar in format to “Dig!,” the 2004 doc comparing the success of The Dandy Warhols with the more tumultuous rise and fall of their friends, The Brian Jonestown Massacre. Here, the negative comparison is ten times more heartbreaking, for we are seeing the life of a beloved rock star through the eyes of his less handsome, less charismatic, and considerably less successful little brother. The envy and self-loathing felt by Tom is at times too palpable to bear, especially when we find out that Matt always had it easier–his parents avow that he was the go-getter, the honor student and athlete, while Tom was a quitter.

Tom–who was thirty when the film was shot–is an overweight, mulleted metalhead still living with his parents in Cincinnati. He’s a better visual artist than Matt, but to date he has only completed a couple of schlocky horror films. He’s invited by Matt as both a roadie and documentarian on The National’s upcoming tour. The goofy, garrulous Tom quickly proves himself to be a disaster at the former task, spacing out about guest lists and food supplies, failing to gather the band members on time. Meanwhile, his constant camera operating and irreverent questions irritate the emphatically humorless crew (the sound engineer, Brandon Reid, comes off as the villain of the film, a sneering, self-important martinet who instantly despises Tom). Eventually, he is fired from the tour.

The tour portion of “Mistaken for Strangers” is the most searing. Matt, a typically skinny, bearded, well-dressed indie rock frontman, carries a moodiness not to be reckoned with, which Tom captures by refusing to shut the camera off during a dozen or so brutal arguments. His anger and depression are undoubtedly the catalyst for The National’s mopey, melancholy appeal, but on a day-to-day level both Tom and the other band members are quelled by it.

The other band members, however, consist of two sets of brothers, who are closer in age (two of them are twins); they have each other when their unpredictable frontman erupts. Tom, who’s accustomed to being the pesky, annoying little brother, has no one to assure him of his self-worth. Throughout the tour, Matt belittles him, lambasting his slovenly habits, his silly sense of humor, his irresponsibility (he’s the bigger drinker of the two). When Tom goes to the other members for guidance, they provide little in the way of comfort; guitarist Aaron Dessner soberly stresses that Tom is an “underdog” and Matt is an “alpha male, so you can never win.” When he returns home, crestfallen, to Cincinnati, his dad tells him that “Matt is more confident, that’s why he’s more successful.”

But just when the film threatens to become a cloying self-pity fest, a silver lining appears. Matt and his wife invite Tom to stay in their Brooklyn home, goading him to finish the film. He has over 200 hours of footage and is ready, as usual, to quit, but Matt hits him with a poignant dose of tough love, and finally we start to see that Matt does admire his brother, that he does see the latent genius in him. Everyone, the audience included, is rooting for Tom despite his maddening inability to grow up.

In making such a personal film, Tom Berninger has expertly demonstrated the pain of being a misunderstood clown in a very serious, very superficial universe; their staggering talent aside, The National and their entourage come off like prissy, image-conscious hipsters, worrying about their hair and whether or not to tuck in their shirts. Some in the audience may want Tom to shut up and regard the band with religious fervor, but I found his rude, bull-in-the-china shop jesting to be a blast of fresh air.

Because Tom is a careless sort, his camerawork is sometimes crude, not to mention self-indulgent; he sometimes features himself in too many shots, especially when he tapes himself crying, an unnecessary ploy for our sympathy. But that very crudeness is what allows him to burrow in the reddened face of his screaming brother, or to illustrate how his brother’s fierceness transforms him into a formidable frontman.

What keeps “Mistaken for Strangers” from being a masterpiece is, surprisingly, its brevity. Tom ended up with an overkill of footage, but he has perhaps clipped too much of it, and some of the themes could be richer. The sibling relationships of the other members, for example, is barely examined: how do they tolerate each other on tour, and deal with creative differences without causing a familial rift? There’s also a lack of depth into how the other members are just as if not more intimidated by Matt, since they have to deal with him more regularly than Tom. But overall Tom’s scattershot approach works. “Mistaken for Strangers” is at once loopy and wistful, a film that rigorously explores the inner workings of jealousy, and also provides the wisdom on how to triumph over it.

(pictured: Director Tom Berninger, right, with brother and National front man Matt Berninger, left, at a National show. (Tribeca Film Festival / September 8, 2011)