How to use nvenc HW acceleration

Dears,

from the given files it's not clear how to enable nvenc HW acceleration. I've tried it with by adding

- "c:v" : "h264_nvenc"_ to the params section in settings.json, but CPU is still used
- found gpu_id parameter in common.py, but i haven't found any reference to it where it would be actually used.
Thank you in advance for your comments
