imaging that you have a avisynth script to run, like this

ffvideosource(...)
eedi2()
eedi2()

you will find that only one core of your cpu is used,
for instance it's 50% on my computer.


You hope that the two eedi2 could run concurrently on the 2 cores
to gain the speed.

You may have a try like this

ffvideosource(...)
eedi2()
sorathread()
eedi2()

now the 2 eedi2 will run on different thread to eat up your cpu power.
one core: ffvideosource and eedi2
another core: eedi2



note: eedi2 is a plugin of avs to make video double height