"It's a movie about music that is unadorned and authentic," said director James Mangold in the latest featurette released by Searchlight Pictures.
"There are 40 songs in the movie that he performs live, on guitar and harmonica and singing live, take after take after take," explained producer Fred Berger.
"It was important for me to sing and play live, because, if I can actually do it, why should there be an element of artifice here? And, I'm proud that we took that leap," said Chalamet.
And Chalamet wasn't the only performer who sang live. Boyd Holbrook (Johnny Cash), Edward Norton (Pete Seeger) and Monica Barbaro (Joan Baez) also brought live music to set.
Watch the trailer for "A Complete Unknown" here.
"A Complete Unknown" is in theaters nationwide December 25.
The Walt Disney Company is the parent company of Searchlight Pictures and this ABC station.