La Vie En Rose (12A)

She was born in the same year as another tragic singer, Billie Holiday, and almost died the same year that she did. But Edith Piaf somehow struggled on into the 1960s, her life a mess of drugs, collapses and, though her most famous song denied it, regrets. What Olivier Dahan's superficial but stylish-looking biopic conveys is the wonder that she made it that far.

To say that the early life of the woman born Edith Gassion was tough would be a comical understatement. The Parisian district of Belleville where she was raised during the impoverished years of the First World War looks so gaunt and grim in Tetsuo Nagata's photography that it could easily be Berlin in 1945. Neglected by her alcoholic mother, the sickly infant Edith was entrusted to her grandmother's care and lived for much of her childhood in a brothel. At the age of eight she went blind, a condition apparently cured after she prayed to her favourite saint, Thérèse.

No sooner was she settled in the brothel as the beloved pet of the prostitute Titine (Emmanuelle Seigner) than her father snatched her away again and took her to work with him in the circus.

Dahan, mercifully, breaks up this portrait of hardscrabble childhood – it would be too much to take in one go – with flash-forwards to Piaf's heyday, though given that her success was entwined with tragedy even the fractured timeframe provides scant relief.

La Vie en Rose can't elude the pitfalls of the biopic, specifically the tendency to sacrifice depth to length in the hope that covering the highlights of the life will somehow explain its meaning. Sometimes the narrative is sketchy to the point of evasiveness. When Edith is discovered performing on a street corner by the nightclub owner Louis Leplée (Gérard Depardieu) and whisked onto the stage, her star seems to be on the rise. (Leplée invents her "Little Sparrow" nickname). But it transpires that Edith is still embroiled with a local pimp, and when Leplée is found murdered in his apartment, his friends start casting the blame on his new protegée. Two major questions are raised. First, the nature of Edith's dealings with the pimp (we never see her take on any clients) and, second, the extent of her guilt in Leplée's murder. Neither is answered.

There is also a rather unsatisfactory handling of the people who surrounded the singer, beginning with Mômone (Sylvie Testud), the scapegrace friend who used to hang around with Piaf when she was singing on the streets. Later, when Piaf is the toast of late-Forties New York, Mômone is still at hand, but now seems to resent her famous friend, and claims that "I could have been Piaf". What happened in between?

Later still, we see Piaf sullen and discontent in a hotel room with a man who turns out to be – hello? – her husband; how he came to sneak into the picture is anyone's guess. This is either an editing fault, or Dahan was concerned that further exposition would burden the already swollen running time of nearly two-and-a-half hours.

What the film does get right is the choice of Marion Cotillard as Piaf. While her resemblance to the singer is apparently accurate, it is not as simple as a straightforward impersonation. Cotillard has talked about the difficulty of miming to Piaf's singing voice: she would jot down the exact moment when she took a breath, then put on the music again and film herself singing to camera. Yet somehow more impressive is her speaking voice, hoarser in the middle years, then cracked in the later, which makes an uncanny match to her performing voice.

The actress is also obliged to convey a startling physical decline. Always a fragile figure on stage, despite that big vibrato in her delivery, Piaf in her thirties was a tiresome drunk; at 44 she was a hunched and tottering old woman; at 47, frizzy-haired and bug-eyed, she was dead. The brilliance of Cotillard's performance is that, even in her girlishness, she suggests the pathos of a woman who knew she was doomed.

The chronological flitting back and forth helps make the performance all of a piece, but renders the arc of the film somewhat crooked. At one point I felt convinced that it had just executed its dying fall, only to see it spring back up for an extra half-hour. I should have realised, of course – Piaf hadn't yet delivered her signature "Non, je ne regrette rien", a song whose whining defiance has never failed to repel me. It's the "My Way" of its day.

Inside the final 10 minutes comes a flashback that could have had interesting psychological resonances if it had been disclosed earlier, but it's just plonked down, without warning. It compounds the impression of sketchiness.

Only once does Dahan manage a convincing link between the inner turmoil and the outer shell, in a long bravura shot of Piaf walking down a hallway, weeping inconsolably at the news of a bereavement, and then stepping through a curtain onto the stage. The details of the composition, the fluidity of the camera's movement and the magical elision between personal grief and "performed" grief are so confidently organised that one detects the shadow of a much subtler film. I wish that we could have seen it.