You can select what you want.
- NVENC is NVIDIA hardware encoding. It works faster but quality low a bit.
- H.264/H.265 Software encoding. It gives better quality, have a lot of settings but uses CPU and works slower.
> software CRF = 12
It is extremely low. I use 18 for most cases.
It is not simple question about corresponding software and NVENC settings to get the same quality. Approximate answer you can get when switching from software to NVENC. As I can see CRF=12 corresponds to 35 Mbit/s.
About astect ratio (AR). In general case it must be the same as in the source.
Looks like you have video with unreadable aspect ratio. So acpect ratio was reset in output video.
You can fix AR by third party tools or use additional encoder options in SVP Encoder-Advanced mode.
In quick manual by pressing button ? I found these options about aspect ratio:
--ovcopts=aspect= sample aspect ratio
--ovcopts=sar= sample aspect ratio
You can use them.