FFMpeg quality degradation when using NVENC

Question

I'm using ffmpeg to encode a folder full of static PNG images into video format. Among other things, I set the quality to 20Mbps and preset to veryslow. Everything works. However, as soon as I switch from the default H264 encoder to NVENC, it seems the quality settings are completely ignored, and I get default (terrible) quality.

How can I fix this?

Answer 1

libx264 and h.264 nvenc don't share all their options. Run the following 2 help commands to list their options:

ffmpeg -h encoder=h264_nvenc
ffmpeg -h encoder=libx264

On mine (v5.0 in win10) h264_nvenc does not support -preset veryslow option.