Freed from the tutelage of his mentor, Adam Sandler, who has been relegated to making movies for Netflix, SNL alumnus Andy Samberg churns out an old-fashioned SNL character comedy.

“Popstar: Never Stop Never Stopping” is a riff on the music videos he popped out while on the show, a “behind the music” mockumentary where all the energy was pumped into creating new videos and absurdly over-the-top concert sequences. “Popstar” is 86 minutes packed with SNL alumni and far too few funny bits to sustain any of them.

It’s a Justin Bieber spoof that loses its nerve, a film that despite the occasional snort of coke or breast or penis shot, is almost shockingly mild-mannered, a PG version of today’s R-rated comedies.

Samberg plays Conner4Real, a pop rapper popular with the teens, captured just at the moment when it all crashes down around his ears.

He’s got the lifestyle, an indulgent manager (Tim Meadows), a publicist (Sarah Silverman) can only carry him so far and a deal with a major appliance company (repped by the omnipresent Maya Rudolph) that spells disaster.

His new record, “Conquest,” will automatically download to every appliance in the Aquaspin line at midnight on its release date. You open your fridge, there’s Conner4Real and Pink singing about “Equal Rights” for homosexuals, with Conner yelping “Not Gay!” in between every line.

Maybe they’ll get the foul-mouthed tune about the “horny like a Stegosaurus” hook-up who wants him to screw over “like we did Bin Laden.”

Conner is king of the throw-away hip hop catchphrase — “Moped music,” “Patrick Stewart money,” “Turn up the beef.”

He’s got an entourage of yes-men, a turtle sitter for his pet tortoise. But that U-2 styled “automatic download” of his new album has disaster written all over it. And the problems only begin with the nationwide blackout it generates.

The downward spiral is connected with Conner’s need to lose his clueless, omnipotent arrogance and make amends to his former bandmates, the Style Boyz (co-writers/directors Jorma Taccone and Akiva Schaffer). Conner needs to be humbled to get back in the public’s good graces and off of the TMZ knock-off CMZ (Will Arnett, Mike Birbiglia and others mercilessly ridicule the low-rent gossip TV show).

But for some strange reason, Samberg doesn’t commit to the off-stage bits. Every musical moment is a winner, as Conner unleashes hologram duets with Adam Levine (and himself) on stage, or startles Pink with his not-so-veiled homophobia.

Off-stage, Conner is more mild-mannered and human than we’d expect him to be. He’s not an idiot, follows his plummeting record sales and cannily accepts a hotter opening act (Chris Redd is Hunter the Hungry). In short, he’s not funny. Those scenes are all truncated and enervated as well, lacking the energy to reach some sort of conclusion.

One killer moment — Conner cannily proposes to his “publicity” movie star girlfriend (Imogen Poots) in a for-TV spectacle that involves live wolves and the singer Seal, with predictably disastrous results.

But those moments stand out because most everything else off-stage is introduced without being developed. The whole movie, with Joan Cusack as Conner’s coke-snorting mom, to the scads of star cameos — musicians and Simon Cowell singing Conner’s praises in interviews, Bill Hader as a roadie, etc — feels like an under-developed sketch that goes on for too long.

MPAA Rating:R for some graphic nudity, language throughout, sexual content and drug use

Cast: Andy Samberg, Jorma Taccone, Sarah Silverman, Tim Meadows, Chris Redd, Imogen Poots, Bill Hader, Will Arnett, Will Forte, Adam Levine, Pink
Credits: Directed by Akiva Schaffer, Jorma Taccone, script by Andy Samberg, Akiva Schaffer, Jorma Taccone. A Universal release.

Running time: 1:26