They reveal details of a "groundbreaking" filming technique being employed by director Tom Hooper, who is allowing the actors to sing live on set, as opposed to miming to a pre-recorded track.
"It's going to be different, for sure," says Hathaway, who plays Fantine. "This is the first time anyone's tried it like this."
Producer Cameron Mackintosh, who was also behind the record-breaking stage production, said: "We have found an amazing group of actors who are completely at home acting through music, and the only way you can make that work is by capturing it in the moment."
"Les Miserables has to feel real, it has to feel immediate," says Hugh Jackman, who stars as Jean Valjean. "There's an emotional level to this that just cannot be created in the studio," adds Russell Crowe, who plays Javert.
The film is due for release on 14 December in the US and 11 January in the UK.