Who’d have thought that Judd Apatow’s true calling is documentary filmmaking?

After a steady decline with each new film that saw him hideously bottom out with Trainwreck, the former king of arrested development comedy returns to form with May It Last: A Portrait of the Avett Brothers, easily his best work since The 40-Year-Old Virgin.

Perhaps unfairly bolstered by quality music from quality human beings, the film — co-directed with Michael Bonfiglio, whose magic probably shouldn’t be underestimated — the chronicle of the Concord, North Carolina band’s general history, tied to the recording of its 2016 album True Sadness, is a joy for Avett fans.

It’s also about as good a recruitment tool for the ignorant and unconverted as could possibly be made. By Scott and Seth Avett’s sides in demo sessions at Asheville’s Echo Mountain Studios or the proper album recording at Rick Rubin's Shangri La Studios in Malibu, the filmmakers capture the siblings’ musical genius with the same gobsmacked fly-on-the-wall awe as viewers are likely to experience.

Certainly, some degree of manipulation is done in the editing process, but one nonetheless wants to believe in such wondrous moments as the organic nature of the creation of “I Wish I Was” — at least as it’s presented here.

May It Last offers glimpses of the metaphorical gem from Seth strumming alone at home to workshopping it in the demo sessions, to Scott contemplating the partially written song and adding his own lyrics, to the band performing it on stage. The instant evolution is enough to want to rank the brothers among the all-time greats.

The writing, rehearsing and concert segments take up much of the documentary and reveal plenty about the Avetts’ talent and character, but the domestic scenes and quick breaks from making music are just as revelatory, if not more so.

Truly thankful to be doing what they’re doing, the frontmen attract fellow honorable folks to their personal and professional lives, but aren’t afraid to call out the commercialism and other questionable aspects of their career, suggesting a self-awareness and worldliness rare amongst creative types.

Blessed with a wealth of footage from their time with the band, Apatow and Bonfiglio do an extraordinary job of weaving these various strands together into an entertaining, enlightening and frequently emotional whole that feels both complete and over all too soon.

Fortunately, the Avetts show no sign of stopping. Maybe Apatow will stick to the path of his intended purpose as well.

Grade: A. Not rated but with some adult content and language. Playing Sept. 12 at the Fine Arts Theatre, 7pm and 9:30pm

(Photo: Oscilloscope Laboratories)