How Joni Mitchell beat some staggering odds to outshine the Laurel Canyon set.

What would be your abiding memory of being rushed in an air ambulance to a Saskatchewan hospital at the age of nine where, in an atmosphere of fear and secrecy, rustling nuns will transport you to the polio ward? For Joni Mitchell it was the view from the plane window. The towns below, she’'d written in her notebook, ‘looked like topaz brooches on the black velvet land’.

She’'s perfect subject matter for DVD – someone whose life and art, even now, remain twisted together in a double helix, and with the exceptional powers of expression and observation to really bring both alive – and never have I seen the medium serve anyone so well. A documentary alone just wouldn’'t have been able to handle it. This hangs together, as DVDs can, like the ultimate magazine feature, full of sub-plots and sidebars and columns of quotation. You can go back and re-examine it from different starting points and come away with a fresh impression every time. Nothing looks cheap or hurried or insincere and every section of the story has been painstakingly explored for any resonance that might shed a light on its subject, along with 30 years of live footage – gauche early TV shows, the tearful outburst at the Isle of Wight, with fellow jazz messengers Pat Metheny and Jaco Pastorius in the 70s, every station on the track.

You forget the sheer scale of the drama, her life rebounding from one enormous – often self-generated – emotional obstacle to the next. There’s fragile stills and cine reels of the teenage girl who’s beaten her illness and turned the full force of her attention to the local dance contests. When she marries the man she hopes will help get her child out of the foster home, you’re drawn to her glassy expression on the wedding day (she'’s 22), her voiceover pointing out she was still “thinking how I could get out of this”. Her manager decides he can’t risk her being choppered in to appear at Woodstock as there’s no guarantee he can get her back for a crucial Dick Cavett Show the following night. Watch her expression again as she listens to her friends Crosby, Stills, Nash and Young – rushed to the programme for a breathless account of their triumphant performance – and then hear her step up to the piano and play the song she’'d written about it that afternoon, with which, as Crosby points out, “she contributed more to the people’s understanding of that event than anyone who was there.”

All those interviewed are awestruck, affectionate and refreshingly free of self-interest – among them James Taylor, some valuable perspectives from Bill Flanagan, and the two men whose careers were kick-started by her, manager Elliot Roberts and agent David Geffen. But Graham Nash’'s contribution is just extraordinary. You can'’t imagine what he went through, either personally or professionally. He describes the feeling of that early morning race to get to the piano with the tacit acknowledgement that his career as a song writer was being completely eclipsed by that of his lover. Later, in immense detail, we get the full story of his marriage proposal and her decision to choose a career instead. “I was looking at this woman who was so beautiful,” he remembers of the night they met, “surrounded by wonderful warm objects of candles and pieces of silk and tapestry and gargoyles. Quite frankly I'’ll never forget that night. Ever. I fell completely in love with Joni right then,” he says, and makes no attempt to conceal that he'’s never quite got over it.

And it ends with Mitchell reunited with the child she gave away at birth (and imagined so exquisitely in Little Green). She’'d become a mother – and a grandmother– in the space of just a few months, at the age of 54. You’'ll have to walk long and hard to find any documentary with an emotional impact like this. It’'s a masterpiece and no less than she deserves.