Margot Robbie, center, in “Babylon.” Scott Garfield/Paramount Pictures

Say this much for Damien Chazelle: He shows his audience exactly what he’s giving them within the first few minutes of “Babylon,” his bruised, black-eyed valentine to Hollywood’s sybaritic heyday. In a whopper of an opening number, Chazelle films the delivery of an elephant to the estate of film producer Don Wallach (Jeff Garlin), a bravura scene of extravagance and excess that ends with not a few bit players covered in pachyderm waste – recalling the famous joke about the guy who cleans up after the circus every day. Asked why he doesn’t quit, he replies with incredulity: “What, and leave show business?”

That’s the animating question of “Babylon,” Chazelle’s lavish, febrile, ultimately ambiguous portrait of American cinema before the moralizing censors and Wall Street moguls got their mitts on a once-glorious tribe of outlaws, reprobates, perverts and pirates. The louche, lusty pioneers of Chazelle’s admiring imagination made movies on the fly, not to send a message but to see how far they could push a medium still in its infancy. Raffish, ungovernable and not a little unhinged, the early settlers of 1920s Hollywoodland were, by Chazelle’s reckoning, a motley crew of wackos and visionaries, prone to self-destruction but also to soaring flights of inspiration and ecstasy.

At least, I think that’s “Babylon’s” point? Quite honestly, by the time this muddled, overcrowded, tiresomely digressive trip finally crashes like so many post-binge hangovers, Chazelle’s point has gotten lost in a self-indulgent, manically erratic shuffle. Once the elephant is delivered, it becomes the centerpiece of a raging party of unfettered drinking, drugging, sex and a near-death. A fetish-y scene of an overweight man and his young date recalls the scandalous life and career of Fatty Arbuckle; the pencil-mustached Jack Conrad (Brad Pitt, in a silky, endearingly sensitive turn) is clearly meant to evoke John Garfield; and Nellie LaRoy (Margot Robbie), the cocaine-addled ingenue who’s plucked from obscurity to become a star, seems to be based on Mabel Normand.

Brad Pitt, left, and Diego Calva in “Babylon.” Scott Garfield/Paramount Pictures

Cinema nerds will find plenty of similar parlor-game diversions in “Babylon’s” characters and their real-life analogues. (Is the director Nellie works with based on Dorothy Arzner? Anita Loos? Alice Guy-Blaché? Discuss!) But for those not keeping score at home, Chazelle keeps what passes for a narrative cracking along at a breakneck but baggily unstructured speed. While Nellie pursues fame and fortune, Manny Torres, a young man she befriends at Wallach’s party, gets his own chance to leave elephant detail. Played by newcomer Diego Calva in a performance reminiscent of a youthful Javier Bardem, Manny is the ethical center of a film that whirls, gyre-like, into the outré reaches of depravity and dissolution.

Part burlesque, part grotesque, “Babylon” takes its pacey cues and shock effects from earlier, much better films: Chazelle doesn’t tell a story so much as string together sequences that alternately quote “Goodfellas” and “Boogie Nights,” without being nearly as horrifyingly elegant or cringe-inducingly pleasurable as either. Like “Singin’ in the Rain,” which the filmmaker will quote literally in a climax that’s meant to be a moving testament to film’s endurance as an art form, “Babylon” takes place at the cusp of the sound era, when the license and licentiousness of the silents gave way to the rationalized – and fatally sanitized – production practices of the talkies. Manny’s big break comes when he rushes from a remote movie location to Los Angeles to replace a camera; he gets back just before the director is about to lose the light, thereby inadvertently discovering magic hour. In a welcome quiet moment, a Louella-or-is-it-Hedda-like reporter played by Jean Smart schools Jack in the ways of graceful aging in a touching speech about obsolescence and eternity.

Such are the romantic touches that give “Babylon” moments of lyrical lift. Elsewhere, it exists in a revisionist dream space in which anarchy and art go hand in hand, even as the body count piles up and up. Robbie plays Nellie as a creature of insatiable appetites – for fame but most especially cocaine – whose jittery, tight-jawed energy fuels the entire cockeyed caravan. Lewd, lascivious, libidinous, Nellie is the heroine of a picture that begins to feel hectoring in its admiration for her most outrageous antics (the difference between madcap and mayhem lies only in a few random letters, after all). Let’s put it this way: If you must see one movie this year featuring projectile vomiting as an indictment of the upper classes, make it “Triangle of Sadness.” Conversely, if you must see one movie this year featuring a pointless and seemingly endless snake-fight scene, “Babylon” is your best bet.

Although Jack, Nellie and Manny are the main protagonists in “Babylon,” Chazelle introduces a third: jazz musician Sidney Palmer (Jovan Adepo), whose travails as an African American in a mostly white medium come to an offensively absurdist head when he’s asked to perform in blackface. Although he’s a welcome addition to the proceedings, Sidney’s storyline gets lost in Chazelle’s frantic intercutting, which becomes a case of diminishing returns as “Babylon” reaches its panicky denouement: a scene featuring a ghoulish Tobey Maguire, in which he seems to be channeling “Boogie Nights”-era Alfred Molina by way of “Nightmare Alley.”

By this point, the pleasure seekers decadently partying their way through “Babylon” have looked to pain for their biggest turn-on. The breathless energy begins to feel exponentially more forced (and, frankly, unpleasant) the harder Chazelle works to sustain it. Robbie delivers a fearless portrayal of a woman trying to outrun the forces seeking to domesticate her, but she’s abandoned by a story that amounts to little more than a mash-up of moments that, for all their high aesthetic and production value, feel shallow and not terribly original. Even “Babylon’s” final moments – intended to be Chazelle’s crowning paean to cinema at its most expressive and transporting – can’t bring the hazy stuff-for-stuff’s-sake into focus.

Like so many recent films – “Once Upon a Time in Hollywood,” “Belfast,” “The Fabelmans,” “Empire of Light” – “Babylon” wants to pay tribute to the medium that brings us all together in the dark. But it also doesn’t miss an opportunity to alienate the audience at every turn. Which, in a backhanded way, might make it an accidentally honest portrayal of a medium that has always wanted to have its coke and snort it, too.