In my experience, "a movie playing" wouldn't be the right description. I never have a super clear image of characters in my head. More like a vague cartoony idea that can morph drastically through-out the book or even when re-reading. Once I see a movie though, I'd have to force the imaginary version back. Without effort, it's probably the actor in my head, but still not super clear.

Environmental descriptions seem a littler clearer and consistent, both man-made stuff, like buildings and vehicles, and nature, but still nowhere near stable.