Hi,
You can run
$ gst-launch-1.0 videotestsrc num-buffers=300 ! nvvidconv ! nvv4l2h264enc ratecontrol-enable=0 quant-i-frames=30 quant-p-frames=30 ! filesink location=a.264
And check the h264 stream through JM decoder. You will see I and P frames are with qp value=30.
It is same in h265 encoding, but don’t know if any 3rdparty tool can be used to show the information like JM decoder.