With just a slight shift in context, Rodgers and Hammerstein’s beloved musical “The Sound of Music” — something almost everyone likes, except, famously, the late film critic Pauline Kael — can become a creepy exercise in enforced cheer.

Intended or otherwise, this seems to be the murky subtext of Sarah McCarthy’s “The Sound of Mumbai: A Musical,” airing Wednesday on HBO2, a fascinating if unsatisfying documentary that profiles some Indian street children who are chosen to sing songs from “The Sound of Music” with an orchestra for a one-night performance at an elite Mumbai concert hall.

Why the children are asked (plucked, really) to do this is never quite clear, except that the well-off founder of the Bombay Chamber Orchestra feels it would be a splendid opportunity to expose some of the city’s poorest children to the magnificence of the arts. The orchestra flies in an actual Austrian, a music professor named Johannes Steinwender, to conduct the musicians and rehearse the young singers. Everyone seems predictably idealistic about this cross-cultural experience. Everyone gets lederhosen and fraulein braids.

So far, so good, so weird.

A precocious 11-year-old boy named Ashish is over the moon about being chosen for the choir. Crammed with his family into a tiny, street-level tenement, Ashish tells us that “the biggest thing” in his life is to become less “self-conscious.” He writes disciplinary lines over and over in a notebook, admonishing himself for his lack of confidence. He practices self-esteem exercises in front of a mirror, a sort of slum kid Stuart Smalley, with Alfalfa’s ear for musical tone — all energy and F-sharps.

“The Sound of Mumbai” wallows beautifully in these contrasts but too easily retracts from necessary documentary conventions, such as theme or point of view. It’s one of those docs that cries out for a few sentences of interstitial text, particularly near the beginning, that might explain what we’re seeing and why.

Ashish wanders the streets of his slums endlessly singing a string of Julie Andrews gaiety. The hills aren’t alive (there are no hills). Nor are there yodeling goatherds. There is noise, filth, hunger. Yet the music fills him with a remote sense of joy and expectation. What there is, thanks to India’s caste system, is a sense of karma that cozies up to part of a lyric from the movie version of the musical: “Perhaps I had a wicked childhood / Perhaps I had a miserable youth / But somewhere in my youth or childhood / I must have done something good.” Ashish pins his hopes on being noticed in the concert, from which his own personal “Slumdog Millionaire” fantasy takes over.

We also meet Ashish’s neighbor and classmate, Mangesh, who offers to help Ashish practice his “Sound of Music” songs. Both boys, also aware of the camera’s presence, try to find polite ways to criticize each other’s singing, obsessed with singing “proper.” When Steinwender chooses Ashish to sing a solo rendition of “The Sound of Music’s” title song in the concert, Mangesh is understandably jealous. Their friendship is ruined.

Ashish’s place in society is made clearer when, during a rehearsal, he hears another group singing down the hall. He wanders in and discovers a roomful of private-school children singing much better than he and his friends can. He becomes instantly smitten with Kimberly, a 10-year-old who talks like a Belgravian debutante. Kimberly becomes instantly smitten with McCarthy’s camera, which she uses to spend time bragging about her studies and extracurricular activities.

Now we are fully in Indiaworld, a place that so powerfully attracts Western journalists and documentary-makers; a place that can often seem to viewers like another planet populated with hyper-competitive strivers who’ve received garbled transmissions from Western pop culture. This is a recent fixation for HBO’s documentary wing, which earlier this month aired the haunting “Marathon Boy” (check listings for encore airings), about an Indian fitness coach who becomes obsessed with training a poor orphan, barely out of toddlerhood, to run extreme marathons and hopefully (inexplicably) become a famous Olympic athlete. There was also “The Bengali Detective,” about a crime solver who dreams of becoming a dancer. Next week, “Pink Saris” explores domestic violence in Indian culture.

Indiaworld can be a baffling, even infuriating place. It’s easy to feel conflicted about the possible happiness the street children derive from participating in the chamber orchestra’s concert — especially when the organizer merrily reminds the camera that the children will always remain poor, because it is their lot in life, but they will always treasure their memories of singing “The Sound of Music” for one night in a posh venue.

The concert itself becomes a melancholy experience for the viewer, with Ashish croaking out his solo as properly as he can and hoping so hard for the world’s approval. His parents sit way up in the rafters in their complimentary seats.

Ashish’s hope of glory and fame instantly fades. The Austrian conductor leaves on a jet home. The smugness of the people who put on the concert — the way they congratulate themselves for their charitable act — is palpable, but McCarthy once more holds back, as if unsure whether what she has chronicled here is supposed to be a story of uplift or a story of oppression. This is one case in which ambiguity loses its allure.

“The Sound of Mumbai” briefly sorts through Ashish’s broken delusions, faintly ending on a note that has haunted us all at one point or another: Rodgers and Hammerstein lied.

The Sound of Mumbai: A Musical

(66 minutes) airs Wednesday at 8 p.m. on HBO2.