This is a music documentary for the connoisseurs and the heads. The Immediate Family is a rock band comprised of five guys in their 70s, a recently formed supergroup of alpha-level session musicians who have worked together for half a century, veterans of the west coast rock and country-rock scene, and who played on records by Linda Ronstadt, Jackson Browne, Carole King, James Taylor, Joni Mitchell and many more.

They are Danny “Kootch” Kortchmar, Waddy Wachtel and Steve Postell on guitar, Russ Kunkel on drums and the massively white-bearded Leland Sklar on bass. These were musicians who benefited from the 70s trend of putting name-check credits in sleeve notes, and so became a professional aristocracy of the recording studio; everybody wanted to hire these easygoing, non-diva musicians who were effortlessly brilliant. They created the west coast sound, or at any rate laid down the foundations for it – the unsung heroes of MOR rock to be heard on every FM station and in every elevator.

But they never got to be stars. Why not? Maybe it’s a drawback of this otherwise estimable film that this question is never explicitly aired, although of course its gallant purpose is to proclaim their excellence and not start undermining or questioning it. It’s not exactly that they didn’t compose; they could write. Perhaps it’s that they were too good, too conscientious, too thorough, and that the real stars had something missing rather than something extra, a kind of gap or fault, a self-questioning for which stardom was the overcompensation.

The Immediate Family are passionate in their creative admiration for Carole King and Linda Ronstadt, though you would be entitled to wonder how female session musicians would have managed. But the Family are always amusing and insightful in their comments and the witty and acerbic Wachtel sounds like a kind of rock’n’roll Larry David.

• Immediate Family is on digital platforms from 3 March.