I’m not sure what I was expecting from Murray Lerner’s The Other Side Of The Mirror – Bob Dylan At The Newport Folk Festival 1963-1965, which I went to see last night at the BFI Southbank last night.

It was going to be fascinating, for sure. That much would have been evident from the clips we’ve seen down the years, most recently in Martin Scorsese’s No Direction Home.

In the event, Lerner’s film, the content of which has been dormant in the vaults for fully 40 years, turns out to be an absolute revelation, one of the best concert movies I’ve ever seen and possibly the best footage of Dylan in performance ever shot.

The film documents Dylan’s three consecutive appearances at the Newport Folk Festival, climaxing with the 1965 electric set that so stunned festival traditionalists, who were appalled by what they saw as Dylan’s betrayal of everything they held most dear and cherished and responded to Bob plugging in with howls of bitter outrage and a lot of loud booing.

Earlier, of course, a lot of these same people were at Dylan’s feet and you can clearly see their adoration on screen as the impossibly young Bob, playing an afternoon workshop, reduces them to admiring awe with a sparklingly playful “All I Really Want To Do” and a grave “With God On Our Side”, on which he’s joined by a fearsomely shrill Joan Baez, unambiguously besotted. By the end of the song, her caterwauling grim beyond words, you’re actually surprised that Dylan’s been able to stop himself from elbowing the hapless woman in the throat to shut her the fuck up.

There’s an absolutely fantastic version from 1963 of “Who Killed Davey Moore?”, whose latent ferocity seems to anticipate the later “It’s Alright, Ma (I’m Only Bleeding)” and a dignified “Only A Pawn In Their Game”, both of which are lapped up hungrily by the Newport crowd.

The change a year later in Dylan’s appearance and relationship with the same crowd is dramatic – the bashful shirt-sleeved boy genius of 1964 has already given way to a sharply-dressed nascent hipster, immediately bantering with the audience, a buzzing livewire. Great footage in this section, too, of Johnny Cash, looking totally fucked on a version of “Don’t Think Twice”.

“Who needs him? He’s sold out,” a belligerent young fuck, full of himself in front of the cameras, announces boldly early in the final section, giving voice to the hostility that later greets Dylan when, fronting an electric band, he unleashes “Maggie’s Farm” and “Like A Rolling Stone”, with Mike Bloomfield astonishing on lead guitar.

Filmed in sumptuous black and white, The Other Side Of The Mirror looks spectacular, and the music is of course great. But what makes Lerner’s film so brilliant is its basic simplicity – it’s mostly just Bob and his songs, with occasional conversational asides. Mercifully, Lerner doesn’t feel obliged to drag in a procession of so-called experts to explain the significance of what we’re watching – and by God, what a relief it is not to have to sit through another pontificating parade of talking heads. Lerner lets the music speak for itself, which it does eloquently and unforgettably.

Don’t miss this when it airs as part of an Arena special this coming Sunday on BBC4, starting at 9.00pm. If you miss that, the DVD’s released on October 29.