Not sure what you mean by 'compressing globally'.

I must admit I don’t know squat about information theory or high powered maths. It just seemed intuitive to me that if you considered the file as a whole and then attempted to find redundant (compressible) sections, you could do nearly as well as considering frames that you have to squash into a certain bit rate.

I guess I should have a play with this compression stuff myself to try and understand it.

Bryan