Use waitKey in order pause and play video

Question

I have a VideoCapture in OpenCV, I can successfully display a given video. What I want to do now is to pause and play by pressing a key (optional which one as long as it works). I have been reading about waitKey but there is something about this whole thing I don't get (ASCII) and how to bind keys. What I understand it is used to let highgui process but can also be used for other purposes?

If it is hard/impossible to pause a video and start it again I would be happy with just a delay when key is pressed.

Help is much appreciated!

Answer 1

With reference to OpenCV Documentation for cv::waitKey(delay), when delay <= 0 will cause to the function to wait infinitely for a key event.

Here is a sample Python script to display frames captured from computer's webcam. When q is pressed, the loop is exited. However, if p is pressed, the display pauses until any other key is pressed:

import cv2
cap = cv2.VideoCapture(0) # getting video from webcam
while cap.isOpened():
    ret, img = cap.read()

    cv2.imshow("Frame",img)

    key = cv2.waitKey(1)
    if key == ord('q'):
        break
    if key == ord('p'):
        cv2.waitKey(-1) #wait until any key is pressed
cap.release()
cv2.destroyAllWindows()