One recent Saturday evening, Ben and I settled down with a bottle of red wine to watch The Last Waltz, the Martin Scorsese directed film of the final concert given by the Band in 1976. We were prompted partly by the news of the death of musician and songwriter Robbie Robertson, but also by my realisation that I had never watched this landmark rock documentary, and lord knows I'm a sucker for a rock documentary.

Ben had seen the film when it came out in 1978. Musically he remembered it as not quite his thing, but some boys at school were referring to it as "important" and he went in a spirit of checking out serious work. I honestly don't think 16-year-old me even knew who the Band were, and if it had been described to me then I would have run a mile.

I used to look through my older brother's record collection in the early 1970s, and was often mystified by cover photos featuring musicians who looked like they came from an earlier century - all beards, and old-timey hats, and gold-prospecting outfits. Were these pop stars, I wondered, or their grandads? Maybe one of those albums was by the Band, I can't remember - but you get the picture. They weren't on my radar.

It wasn't until years later that I heard tracks such as "It Makes No Difference", and "The Weight", and fell in love with Levon Helm singing from behind the drum kit, and those rooted grooves and sweet harmonies. I knew that while I might not love every second of The Last Waltz - I thought maybe there would be a bit too much instrumental noodling, a few too many songs about long-ago battles - there would be plenty I'd enjoy.

And sure enough, I loved loads of the film. I now thought they all looked great, and realised I've become nostalgic for that lived-in look of the 1970s rocker - an image owing more to cigarettes, bourbon and long hours on the tour bus than is nowadays the norm. And I felt nostalgic too for the theatrical grandeur of the venue - the Winterland Ballroom in San Francisco, long since demolished. It reminded me of the London Lyceum, where I saw so many gigs in the late 1970s and early 1980s.

So with my red wine, and my comfy Saturday-night armchair, I was feeling thoroughly mellow and full of laid-back goodwill, when on walked Joni Mitchell, to take everything up to another level.

The timing was a stroke of film-editing genius. Moments before there had been a scene of the band members lounging backstage and chatting about the "benefits" and sexual opportunities of being on tour. I'd been anxious, thinking, "Oh be careful, lads. I like you, don't say anything too awful here." And they don't, not really, it's all just of its time - men being men. Briefly there's a lot of testosterone in the air, and a reminder of the old rules of rock 'n' roll - and then we cut back to the concert and on comes Joni.

She's wearing a flowing skirt and a tight T-shirt, and some kind of ornate silver eagle necklace. When Joni straps on her acoustic guitar and starts playing you feel the confidence burning off her like a flame. She's spotlit, and in the shadows Rick Danko watches her with a look of sheer awe on his face, bless him.

I sat up straight in my armchair thinking, "OK, we've gone somewhere else now," and it's not just the precision and swagger of her diction, the intricacy of the chords, the detail in the lyrics - though it is all those things - it's the realisation that while the music we've heard up until now owed a huge debt to previous genres and traditions, Joni had invented a whole new genre of her own.

And, of course, after that scene of the guys talking about chasing women, the song Joni sings is "Coyote". On the surface the lyrics are describe a predatory man - "He pins me in a corner and he won't take no" - and a player, who's "got a woman at home/He's got another woman down the hall/He seems to want me anyway." But in the end, as so often in Joni's songs, she's the one calling the shots. The song is a farewell with "no regrets".

Well, the film is worth watching for that five minutes alone. Although there are plenty of other great moments, including a verse from Mavis Staples, and Bob Dylan in an excellent hat. And, of course, Robbie Robertson's lovely face, which Joni fondly strokes in a moment of tenderness captured forever in this elegiac film.