Dave92F1's profile - activity

In Python, poll with cv2.getWindowImageRect(windowName). It will return (-1, -1, -1, -1) when the user clicks the window

Is there a way to control the video codec encoding bitrate in OpenCV?

With ffmpeg you can do -qscale n. That will (indirectly) influence the bitrate. Is there an equivalent via the OpenCV Python bindings?

The bitrate I get now seems to be around 8 to 10 Mbps, which is really high (quality is excellent of course, but I'm trying to save on bandwidth...)

Is there a way to call WaitKey without incurring a (minimum) 1 millisecond block?

Suppose I have a 300 frames/sec camera & display - to display each frame I need to call waitkey(1) 300 times each second (because you have to call waitkey to get imshow to work), which consumes 30% of my entire CPU.

Most of that time is just sitting there waiting for the keyboard, at 1 ms per call.

This seems like a huge waste of CPU time.

Is there some way to call WaitKey without the needless wait-for-keyboard delay?

WaitKey(0.0000000001) I suppose would do it, but WaitKey only takes integers...

How can I check if a new frame is available from the camera (without waiting for it)?

If I do a cam.grab() it always returns True, even if I just retrieved a frame an instant before. If I then do a cam.retrieve(), that call blocks until the next frame is ready (wasting CPU time that I need for other things).

If I call cam.read(), that also blocks until the next frame is ready from the camera.

How can I check if a frame is ready without waiting for it?

I'd like to do something like this:

while True:
  if cam.newFrameReady()
    frame = cam.read()
    [do something with the frame]

  [do some other stuff while frame is not yet ready]

Is there a way to do this in Python?

FWIW, I'm on Win7 using a DirectShow camera.