saying things are just bad doesnt help me or you at all....

you have to at least say what you are doing, and how you are doing it.

i didnt change anything to affect performance - you need to tell me what you did.

I use sync there is a bug that woun't re-sync after the loop it's finished , that's ( I think ) it's not about macmini or macbook . Pls check your self .
what do you see?

what do you mean re-sync after movie finished?

How long - in frames - is each movie?

I dont see anything you describe here.