Formed in 2016, the South Korean group has become a global sensation, and the documentary, directed by Caroline Suh, essentially builds toward their triumphant performance at Coachella in 2019.In introducing the four members individually and collectively, the project also offers a humanizing glimpse at the tradeoffs made to achieve this success, coming up through the ranks of YG Entertainment, which churns out acts while screening candidates for the elusive qualities associated with stardom.That includes a training program that begins when the contenders are at most in their early teens (Suh incorporates audition videos), and when the practicing begins in earnest, a schedule that allows one day off every two weeks.While the stars of Blackpink — Jisoo, Jennie, Rosé, and Lisa — express the requisite enthusiasm for performing, the film really distinguishes itself when the women let their guard down a bit, going beyond the platitudes. There’s an element of wistfulness, for example, when discussing not growing up with their families, missed experiences, or feeling alive while on stage and a degree of emptiness in the quiet that follows.”A lot of people make memories as a high-school student,” Jennie says. “But I never had that.”The members also acknowledge the pressure and expectations they currently face (“How do we live up to this hype?” their producer asks) and the potentially fleeting nature of fame, including the prospect of being shunted aside for some new act when they’re older.”The thing is, you can never tell how long it will last,” Rosé, who was raised in Australia, muses at one point.Of course, the all-female quartet remains in their 20s, with hits like “Kill This Love,” and the moments of sobriety don’t make “Blackpink: Light Up the Sky” a downer by any means. There are still plenty of boisterous performances showcasing their talents, behind-the-scenes access to rehearsals and car rides as they crisscross the globe, and even a few happy tears during a show.For Netflix, aligning itself with popular music acts is clearly a no-brainer — witness its Taylor Swift documentary “Miss Americana” earlier this year — and a way to broaden its demographic appeal.Nevertheless, given that this kind of documentary is as much a marketing tool as anything else — both for the streaming service and the group’s new album — the challenge is to make it more than just an infomercial. Seen that way, “Blackpink: Light Up the Sky” manages to offer a welcome reminder that even for K-pop’s reigning queens, all that glitters isn’t always gold.”Blackpink: Light Up the Sky” premieres Oct. 14 on Netflix.