If I said "I've just dipped into the book", I would mean something like "I've had a quick look at some of the pages of the book". The idea would be that I've looked at the odd page to see what the book was about.
In what way can you 'dip into' a film? "I saw bits of the film while I was waiting in the doctor's surgery" or "I saw bits and pieces of it but I kept falling asleep."
That's how I see most films nowadays.