Cate Blanchett is ''very impatient.''

The 49-year-old actress may have directed numerous theatre productions over the years but she has admitted it would have to be something magical for her to agree to take the reins of a movie because the process is so long-winded.

Speaking to talkRADIO at the premiere of 'A House With A Clock in its Walls' in London on Wednesday (06.09.18) night, Blanchett said: ''I'm very impatient.

''So to get a movie, to cast it, to location scout, to shoot the thing, to edit the thing, to publicise the thing takes an awfully long time so it would have to be something I'm prepared to stick with for that long.''

The blonde beauty - who has kids Dashiell, 16, Roman, 14, Ignatius, 10, and Edith, three, with her husband Andrew Upton - is also very particular about what film roles she takes on because they have to fit around her children's schooling.

However, she has admitted it was a ''no brainer'' when she was asked to play Mrs. Zimmerman in the forthcoming thriller because she wanted to star alongside comedian Jack Black and be directed by the ''fantastic'' Eli Roth.

She explained: ''I'm so free-wheeling about what I decide to do, a lot of it is based on my children's school schedule, but when this came up, I loved the script, I knew the book from my childhood. And then when I knew Jack was going to be in it and Eli Roth - who is not only a fantastic director of horror, an amazing actor and extraordinary cinephile - was going to direct it, so it was kind of a no brainer.''

And Blanchett is confident that the film will do well when it hits cinema screens later this month because they all had so much fun shooting the horror scenes.

She said: ''Sometimes you're on a movie set and the situation is difficult, not that there are any personality problems, but the filming is difficult but the movie ends up being good or sometimes you have a great time and the movie doesn't do so well. I think this was the best of both worlds because we all got on, the atmosphere was fantastic, it was buoyant but we took the work seriously - we had fun. And the movie is really good.''