Setting process priority so it runs when screen is locked

Hello Experts,

I run some CPU intensive processes (video encoding using X264) in a
command shell. Since I don't want it to affect my normal foreground
applications, I set it to IDLE/BELOW_NORMAL priority using Process
Explorer. However, when I lock my screen (manually or automatically
after some idle time), the encoding virtually stops. When I unlock my
screen, I can see from recent history that CPU was idle instead of
being utilized to run the encoding process. What can I do to ensure
that my background encoding process continues to run even when I am
away from the computer (the screen is locked), but at the same time
not affect any foreground applications if I happen to be using the
computer?

Thanks

P Adhia