Ported #14538 here.

Please fix this warning:

object_detection.cpp(85): warning C4244: 'initializing': conversion from 'double' to 'float'

@dkurt
This is a very good improvement for detection performance.

• It works well for VideoCamera, because FPS is limited.

• But it works a bit strange for video files - very high capture_fps = 256 FPS, a lot of skipped frames. A five-minute video file is played in a several seconds. Everything flickers very fast on the screen.
  Perhaps better to limit the capture_fps = max(detection_fps, videofile_fps).

@AlexeyAB, thanks! That's a good point. Feel free to propose a PR or open an issue.