H264_nvenc error

On Jetson platforms, we only enable hardware decoding in ffmpeg and the implementation is based on jetson_multimedia_api. Please refer to developer guide and the topics:
Jetson TX2 and FFmpeg - Can't initialize nvrm channel - #5 by DaneLLL
Hardware accelerated video playback with L4T ffmpeg - #7 by DaneLLL

If you need hardware encoding, may check the community contribution mentioned in:
Jetson Nano FAQ

Q: Is hardware acceleration enabled in ffmpeg?