For one that camera angle makes it sort of tough to see how much lateral sliding is actually taking place. So you could be chasing your tail here.
Jim already answered the question. The hips need to move far enough to the left so the right shoulder can unwind on the right plane. The actual amount of sliding might vary from golfer to golfer and feel is often very different than reality, i.e. trying to exactly quantify the amount might not do the golfer any good.
For example, if I am struggling with this area, Brian might say try and slide the hips about another '2 inches.' OK, I'll try and do that. Then I swing again, and he says, "Almost, but you need more." So again, what I felt was '2 inches' is going to feel maybe like three of four inches even though (if we could track such a thing accurately) my hips are indeed only traveling the prescribed amount.