Comment by throwaway4PP

It’s crude, but you can overcome the degraded quality imparted by gpu accelerated encoding by specifying a higher video bitrate.

Find a complex short scene in your cpu encoded video, extract it, ffprobe it to get average video bitrate, and take the same clip in raw and try gpu accelerated encoding at +20% bitrate. From there, iterate.

For a friend’s use-case that I helped with, +30% video bitrate bump overcame the degraded vquality.

Edit: strangely enough, if memory serves, after the correcting +30% was applied the actual ffprobe bitrates between the videos were very similar, maybe a 10% or less difference. Someone smarter than me can work that logic out.