Originally Posted by Stephen Warren
Could you run nvidia-settings and look at the PowerMizer page while decoding the video, and running the CPU at 1GHz and 2.5GHz. Is the selected PowerMizer level different between the two runs?
Just a single PowerMizer level is displayed in nvidia-settings, I can't change it. And it also remains the same all the time, whether the CPU runs at 1 GHz or 2.5 Ghz.