What determines video bitrate and rate-control method if do not specify in FFmpeg command while transcoding a video?

I have been transcoding videos with the following FFmpeg command, I am not passing any option related to rate-control methods, and i am wondering what determines the video and rate-control method for the following command.
ffmpeg -threads 1 -hwaccel auto -extra_hw_frames 3 -i [input] -map 0:a? -map 0:s? -map 0:v -c:v hevc_nvenc -qp 22 -movflags +faststart “[output]_HEVC.mkv”

Hey, Encoding options differ from codec to codec but FFmpeg uses information provided in terms of options to determine the rate control method.

Can you please elaborate it more, I am unable to get your point.

When you use -qp quantization parameter with the transcoding command FFmpeg assumes Constant QP (CQP) as the rate control method. I hope now your confusion is resolved.

Here, the -crf parameter denotes the use of the Constant Rate Factor (CRF) rate control method, and when you specify video bitrate with -b:v parameter it assumes the Variable Bitrate (VBR) or Constant Bitrate (CBR) rate control method depending on other options used with it.

Thanks for your suggestions now all the doubts are cleared Thanks Gumlet community.