Jack Black in Margot at the Wedding Ken Regan/Courtesy of Paramount Vantage

The shaky, grainy camera work obviously it recalls a home film from the '70s. Jennifer has mentioned that you used these really specific lenses. Is that an attempt to make it more intimate so the viewer realizes that you're looking at a family situation, and to get back to the 70's, a period that must have been quite formative for you?
Well, I didn't think deliberately about the '70s. But it's certainly true of a lot of movies in the '70s. I was talking to Harris Savides, who shot the movie. I was describing how I wanted the movie to look. And he was the one who suggested those lenses and so we did these tests. And there's no other way to explain it except that it looked like how I imagined, so that made that decision easy. But I really wanted you to feel the film quality of it, because, like you say, I think it's something that's true of older movies. A lot of movies now are digitally enhanced and even if they're shot on film, they do digital intermediates where they can manipulate everything. And Harris and I both really liked the roughness and rawness of film and so that it just seemed right for the movie. I wasn't trying necessarily to capture any specific look. We thought about old photographs — an old photo from the '70s — the kind of washed-out color of photos. And also I wanted it to be how your eye sees in real life. When you're inside a house without the lights on, and there's light coming in the window, people tend to fall in the shadow in real life, unless you turn on another light. Often in movies they'll supplement so you can see their faces better. But I didn't want to do that. So it's really the available light: the dashboard of the car or a street lamp or porch light or something like that. We really shot these things for what they were.

Jack Black is not an actor you would normally associate with his character. So he's cast a little bit against type. Why did you settle on him?
I wanted somebody who was funny and also who was a good actor. And Jennifer had known Jack for a little while, and I'd met him a few different times. And he just had a quality in real life that I thought seemed right for Malcolm. And I also wanted to use his humor. But I think a lot of times comedians get cast in serious parts, and they're asked to play it almost without any comedy. They're asked to play it dead serious. And I wanted to take advantage of the fact that I had Jack Black, because Malcolm was written as a comic character. But allow him to be funny in the realm of the movie and the reality that this movie could hold. And I had no question that he could do it.

A woman on a train with her son was the inspiration for this. Is there another film that has popped into your brain since?
I have. Yeah, I have lots of them. I'm writing something now but they don't all necessarily come like that. Sometimes it's a character idea.

Do you have a couple of things on the boil at once?
No, but I'll take notes all the time so some things come up and stay with me. A lot of times things will come up and then two days later, there's no traction. But if I have an idea that stays with me for weeks or months — even if I'm working on something else — I'll know that it's there, and I can come to it when I've got the time or I'm ready to. But sometimes it's not that specific. Sometimes it's just a conversation, and I'll write a conversation between two people and suddenly that will inform who these people are and where they are and then it'll all build out from there.