the chop increases as processor space is used up more.
less processes, less chop, more processes and more chopping.
viewing a video in a smaller window decreases processor demand, less choppy.
viewing a video full screen is more process demand, more choppy.
The problem happens more with single core processors, as the number of cores increases, the less likely you are to overload the cache of the processor.
Today's applications are using more and more memory and processor cache. This is why many people are moving over to multicore processors.
Another way to approach it, eliminate as many excess programs from the computer as possible. Free up as much processor cache as possible.