It is possible that you know Howard Ashman’s work better than you think you do. Along with composer Alan Menken, Ashman was the Oscar-winning lyricist whose songs revived the dwindling reputation of Disney in the 1980s with The Little Mermaid.

The result reinvented the art form that put Disney on the map but had since become so sidelined that the studio had placed its animation studios three miles down the road in a car park, which is where Ashman set to work after he was persuaded to move there.

According to Don Hahn’s new documentary, which is constructed entirely from archive and off-screen interviews, the conversation that pushed Ashman from east coast New York to west coast Hollywood took place during Pesach.

Ashman’s journey up to that point had featured professional highs including Little Shop Of Horrors and one fathom-deep low with the beauty pageant musical Smile, written with Marvin Hamlisch. But it all started modestly in Baltimore.

The son of a delivery driver, Ashman intuitively constructed his own shows in his bedroom, according to his sister, Sarah Gillespie. Toys were conscripted into stories; lighting would be modified with a cloth over a lampshade. It was all good practice for when Ashman would eventually set up his off-off Broadway theatre in Lower Fifth Avenue, 1970s New York.

People said he was crazy. New York was a much more dangerous place then than it is now, and this part of town was so scary at night people just wouldn’t go there. But as was usually the case with Ashman, he knew better.

Hanging over Hahn’s film is an almost unbearable poignancy. We know early on from studio footage of Howard recording his and Menken’s score for Beauty and the Beast, in which the composer is seen working with one of the animated feature’s actors Angela Lansbury, that it doesn’t end well.

“It was the summer of 1990 and we were all gathered in New York City to record the songs for Beauty and the Beast,” explains the voice of Hahn, who was also the producer of the film. Ashman seems in his prime. Little did anyone know that nine months later he would die of AIDS.

The film isn’t only a portrait. It gives a sense of how difficult is the process in creating work that the public consume as casually as a stunning landscape viewed through the window of a speeding car. Menken recalls how Ashman threw a top-of-the-range Walkman Pro against the wall because the mic wasn’t working very well. By then Ashman knew he was dying, and the sense of not being able to achieve all he wanted in the time he had left was eating him from the inside, much like the disease.

But even more illuminating is a recording from an earlier part of Ashman’s life when he was working with Hamlisch on the hugely promising yet ill-fated musical Smile. The two did not get along as well as they might. And as Hamlisch filibusters his way through the conversation with florid bursts of piano, you can hear Ashman trying to articulate what was wrong with the song they were working on.

It was the aftermath of that show’s failure that caused Ashman to head for Disney, pushed by a phone call from Disney executive Jeffrey Katzenberg.

“I’ll never forget that we were having Seder at Howard’s apartment,” remembers his sister Sarah.

“It was the middle of Passover, and Jeffrey calls in the middle of the Seder. Almost like Elijah. And Howard takes the call because he knows it’s Jeffrey who is saying ‘When are you coming? When are you going to sign?’”