https://en.wikipedia.org/wiki/Nvidia_NVENC
https://trac.ffmpeg.org/wiki/HWAccelIntro#NVENC
Example use:
Use NVENC for transcoding MPEG2 (MOVIE-raw.mkv) to X264 with ffmpeg. The sound (ac3-sound) is just copied.
Without nvenc:
ffmpeg -i MOVIE-raw.mkv -vf "crop=720:416:0:80" -map 0:0 -map 0:1 -map 0:2 -map 0:3 -map 0:4 -map 0:5 -c:v libx264 -crf 18 -preset veryslow -tune film -c:s copy -c:a:0 copy -c:a:1 copy enc-MOVIE-raw.mkv
result: frame= 1626 fps= 48 q=-1.0 Lsize= 12518kB time=00:01:05.05 bitrate=1576.3kbits/s speed=1.93x
with nvenc: