Another Day, Another Time: Celebrating the Music of Inside Llewyn Davis

Concert documentaries are a tricky prospect for reviewers. The genre has produced plenty of culturally significant works (Gimme Shelter, The Concert for Bangladesh, The Last Waltz) and many storming, memorable performances (AC/DC: Let There Be Rock, Stop Making Sense). Cinematically speaking, however, the concert doc is necessarily bound by its theatrical underpinnings.

And then there's the Hawthorne Effect: when musicians know they are on camera, a polished professionalism kicks in. All hopes for rough edges and unexpected detours – the imperfections that often make for a properly electrifying performance – are dashed thoroughly.

Another Day, Another Time doesn't exactly transcend the problems inherent in the form, but the roughhewn, grassroots nature of the music (folk, gospel, bluegrass) does offset the potential for overly sleek renditions.

The idea itself is an oddity – a film based on a concert based on the Coen brothers' Inside Llewyn Davis, which in turn is loosely based on the autobiography of 1960s folk singer Dave Van Ronk. Another Day is immediately hampered by the lacklustre box-office performance of its parent project. In common with the Coens' film, it deserves a wider audience.

As usual, the concert itself is supplemented by backstage vignettes. And as usual, the performances are reliably excellent. Watch out for Avett Brothers' toe-tapping How I Got to Memphis, Lake Street Dive's sassy You Go Down Smooth, and Oscar Isaac's Green, Green Rocky Road. The Coens beam like proud parents from the sidelines.

There are lovely old standards performed by new folkies. Gillian Welch and Dave Rawlings belt out Let the Circle Be Unbroken, The Punch Brothers do great work with The Auld Triangle. The stairwells of New York's Town Hall provide a touch of historical context, as does an appearance by Joan Baez. "She's fucking Joan Baez, you know!" cries an awestruck Marcus Mumford.

All we need know is Patti Smith doing Power to the People. And here she comes.

Can Another Day do for '60s folk what the Coens and regular collaborator T Bone Burnett's O Brother, Where Art Thou? did for bluegrass? We do hope so.