The musical biopic is a staple of the Hollywood economy. Like an Airfix model kit it comes with the necessary parts presupplied: sex, drugs and a soundtrack. All the director need do is glue them together. Actors are keen too, as portraying musicians is like prospecting for Oscars: in recent years the lives of Edith Piaf, Ray Charles and Johnny Cash’s wife June Carter have all won statuettes for their stars.