what is constant qp in nvenc?

Hi, i’m using nvenc with ffmpeg.

-rc E…V… Override the preset rate-control (from -1 to INT_MAX) (default -1)
constqp E…V… Constant QP mode
vbr E…V… Variable bitrate mode
cbr E…V… Constant bitrate mode
vbr_minqp E…V… Variable bitrate mode with MinQP
ll_2pass_quality E…V… Multi-pass optimized for image quality (only for low-latency presets)
ll_2pass_size E…V… Multi-pass optimized for constant frame size (only for low-latency presets)
vbr_2pass E…V… Multi-pass variable bitrate mode

you can see constqp options and default is -1.
So, -1 means adaptive?
The encoding result of constqp -1 seems adaptively constrol the QP value.
Is it correct?

To set specific rate control mode using NVENC, please use NVENC-specific options after setting the codec to h264_nvenc (-rcmode ). If you do not specify the RC mode in NVENC options, it gets set up automatically depending upon other options on the FFmpeg command line, which may or may not be a desirable outcome. Hence we always recommend setting the explicit rate control mode via the NVENC command line.

Hi, thank you for your comment.
But, what i was exactly wanted to know is what is “-qp -1” and how it works.
If you know answer, please let me know.

When i tested “-rc constqp -qp -1”, it works like adaptively control qp factor to minimize bitrate.
but the quality of video is quite good.