starstarstar-half(2.5 stars)

It’s the last day of business at a scruffy Las Vegas dive bar called the Roaring 20s, and the regulars have gathered to pay their respects. Shuffling in one by one, they greet one another with practiced familiarity: Think “Cheers,” by way of Charles Bukowski and Tom Waits.

As “Bloody Nose, Empty Pockets” opens, viewers may think they’re settling in for a cinema verite deep-dive into the kind of American subculture documentarians regularly plumb for material, their prurience only thinly veiled by claims of sociological interest. But sibling filmmakers Bill and Turner Ross are up to something sneakier. In reality, “Bloody Nose, Empty Pockets” wasn’t filmed in Las Vegas, but in New Orleans, in a bar that the team dressed themselves and populated with locals they discovered in nearby watering holes, then filmed over 18 hours in a hybrid exercise in staged spontaneity, calculated improvisation and dramatized documentary.

The result is an absorbing portrait of drinking life in all its joys — fellowship, high spirits and fleeting, flirty intimacy — and sorrows. Anyone who’s been a barfly for any period of time (guilty) will recognize the arc: An evening that begins with witty banter and free-flowing alcohol can devolve into maudlin self-pity and outright hostility faster than a bartender can yell, “Last call.”

Those evenings can also be monumentally boring, as “Bloody Nose, Empty Pockets” reveals even as the filmmakers keep the action moving as best they can. The sharpest character in the film is a barkeep named Marc, who opens the Roaring 20s in the morning by giving the bar mascot, a thoughtful former actor named Michael, a much-needed eye-opener. When Marc ends his shift with an unsentimental flourish, a patient, seen-it-all single mom named Shay takes over, acting as den mother while the joint fills with revelers in various stages of inebriation. Although there are more than a few laughs in “Bloody Nose, Empty Pockets” (there’s a particularly amusing bit involving the creative use of the house phone), it’s no surprise when tears are shed, most affectingly by a veteran named Bruce, who comes to the Roaring 20s because there’s no place else to go.

As the night gives way to the wee hours of morning, “Bloody Nose, Empty Pockets” takes on the queasy feeling of staying — and staring — too long at the fair. Although the film never engages in mockery for its own sake, viewers are forgiven for feeling they’re bearing witness to people at their most vulnerable, in service to ambiguous ends. As an amalgam of fly-on-the-wall filmmaking and live theater, this is admittedly a fascinating artistic experiment. The humanistic point is more difficult to discern in a movie that teeters on an uncomfortable knife edge between compassion and human-zoo voyeurism. Still, there’s no denying that the wise, funny, loving protagonists of “Bloody Nose, Empty Pockets” make for unforgettable company, even after the hangover has worn off.

Unrated. Available July 10 via Film at Lincoln Center’s virtual cinema. Contains profanity, alcohol abuse, smoking and brief nudity. 98 minutes.