Questions about ROI profile Settings and video coding results(ROI encoding with 01_video_encode sample)

Hi, we tried H.265 based ROI encoding in JP4.5 (using jetson_multimedia_api), but I have a few questions to confirm.

  1. About ROI configure
    Does it support setting only one line of arguments in ROI.txt that supports ROI encoding for a video, or can you only set ROI for each frame?
  2. About QP delta
    (1) When the QP delta of ROI was set to a negative value, the desired result was indeed achieved, and the ROI showed a clear effect. However, we found that the size of the video encoded with ROI was larger than that encoded with only H.265.At this point, we are confused about how Nvidia’s hard-coding mechanism works.Theoretically, ROI should reduce the code stream, not the other way around.
    (2) When the QP delta of ROI is set to be positive, we find that the whole result changes. Although the code stream is reduced, the whole video picture becomes worse instead of the area of ROI becoming blurred.So can QP delta only be set to negative?
  3. About MINQP and MAXQP
    In CBR mode, we found that when we set MINQP and MAXQP, the output Average QP value is not necessarily between the two values. What is the reason?
    I don’t understand why the ROI coding effect is inconsistent with the theoretical conclusion, or is there something wrong with my usage?As for these questions, I hope you can give some reasonable explanations.
    Thanks