Emma Thompson plays Travers, the curmudgeonly author of "Mary Poppins."
"It's a good movie. I think it's a really good film. I mean, I've seen it three times and it moves me each time," said Thompson.
Walt Disney, played here by Tom Hanks, had promised his daughters he'd make "Mary Poppins" into a movie. He just never thought it would take him 20 years.
Hanks says Disney knew how to run his operation: he hired people who loved going to work as much as he did.
"What he had here was long-standing employees that would stay for years and years and years and years and churn out their absolute best work," said Hanks.
Songwriter Richard Sherman was an advisor on the film.
"The whole picture just rings of the truth. It all happened," said Sherman.
Sherman and his brother, Robert, wrote the now classic songs in "Mary Poppins," including "Supercalifragilisticexpialidocious."
The stars of the 1964 film weren't really informed of all the drama leading up to making the movie.
"It's a wonderful back story that I never knew anything about, so the movie's a sort of revelation, or when I saw it, was a revelation for me. I have seen it and I think it's wonderful," said Julie Andrews.
Dick Van Dyke said Travers was never on the set.
"I think I met her at the premiere. I knew he was having a problem, but I had no idea until I saw the movie how big a problem it was," said Van Dyke.
Travers did not want Van Dyke in the movie. "Saving Mr. Banks" opens in limited release on Friday.