Highly skilled specialist editors produce two-minute promos that can make or break a blockbuster. We step inside their hidden world

A few years ago, a Hollywood studio approached the tech giant Ibm with an idea. Perhaps it would be fun if Watson – the company’s artificial intelligence system – analysed its new film about an artificial humanoid gone rogue, and created a trailer for it. The technology was duly “trained” on 100 horror trailers, fed the 90-minute film, and a human editor helped stitch its chosen clips together.

The result, billed as “the first movie trailer made by AI”, is awful. The exchanges are slow and pause-filled, as though filmed underwater. Toby Jones raises his eyebrow sagely at nothing. The screen flashes to black for no reason. At the end, the title card apologetically fades in: “Morgan … September 2.”...