A documentary should earn the viewer’s credence. The notion that vérité can be culled from cinéma has always been a tenuous proposition. Notwithstanding its ability to record objective phenomena, the camera is forever subjective, based on the wiles of the person holding it and, especially, those who subsequently piece together the film. Skepticism is warranted and necessary.

While this may seem like old news, there are moments when even the most diligent documentarian can’t help but tip her hand and, having done so, make us wonder about the movie’s overall integrity. 

Director Rita Baghdadi’s “Sirens” isn’t the most egregious example of this tendency; in fact, only the most callous of souls would question its probity, particularly given the extremities endured by the film’s protagonists. All the same, a smidgen of doubt is sown when stagecraft calls attention to itself.

“Sirens” chronicles the ongoing travails and occasional successes of Slave to Sirens, a thrash metal band based in Lebanon. There are, as you might guess, more accommodating locales than Beirut for this peculiarly intensive genre of music, particularly when taking into account that the players are all women. Ms. Baghdadi brings her focus to Shery Bechara and Lilas Mayassi, respectively the group’s lead and rhythm guitarists.

What, exactly, is the relationship between Ms. Bechara and Ms. Mayassi? Their camaraderie as musicians is clear from the get-go — both comment on a shared chemistry — and, while there are intimations of romance, the state of things is left naggingly ambiguous. A certain trepidation is understandable. In one scene we overhear the government policy on sexual relations that “contradict the laws of nature.” Same-sex relationships are, to put it mildly, not smiled upon.

This of course doesn’t stem the tide of attraction or love. At the midpoint of the film, Ms. Mayassi discloses that she has begun an online relationship with a Syrian woman, one she goes to inordinate lengths to hide from her mother and seemingly the rest of the band. In the meantime, Slave to Sirens is undergoing a crisis of personality and direction. Musical differences escalate, and before long Ms. Bechara hands in her resignation. 

Friction between bandmates is one of the many universal tangents glanced upon in “Sirens.” What’s specific is the locale and the climate of anxiety it engenders and has, in fact, engendered for more than a generation. Ms. Baghdadi punctuates the film with footage of demonstrations, riots, rubble-strewn thoroughfares, and, largely through the mulling of Ms. Mayassi, the psychological costs of having come of age in a country beset by political oppression and social unrest.

Interiority is a difficult aspect of human nature to capture on film. Blatant emotions can be registered, even taking into account the degree of self-consciousness that comes with having a camera trawling the room, but states of mind are trickier. This is where Ms. Baghdadi errs on the side of the theatrical, placing the camera in unlikely positions or staging tableaus that have less to do with psychological disclosure than with artistic over-interpretation.

When, for instance, Ms. Bechara is seen reclining on an outcropping of rock in her fishnet and leathers, a rueful voiceover is undercut by the glamor of the pose. At another moment, we watch Ms. Mayassi, in bed, strumming her guitar and brooding intently. The camera assumes an ascending bird’s eye view, and we can’t help but wonder: How on earth did Ms. Baghdadi get her camera up there? Modern technology makes for incredible flexibility of vantage points, sure, but at some cost to verisimilitude and intimacy.

Such moments are few and far between, but they niggle all the same. Would that Ms. Baghdadi had spent more time with Maya Khairallah, Alma Doumani, and Tatyana Boughaba — that is to say, the other members of Slave to Sirens — and, especially, with Ms. Mayassi’s mother, who brings a welcome grounding to the self-involvement of the creative types surrounding her. In the meantime, struggling rock ’n’ rollers here in the West should take note and be humbled by the audacity and determination of the young women at the core of “Sirens.”