OpenCV Video capture using keyboard to start/stop

Question

I have a running script capable of starting/stopping a video stream using 2 different keys;

• Program runs and shows the live stream.
• When ESC is hit, the program exits.
• When SPACE is hit, the video stream is captured.

However, when a video is captured it stores all the stream from the beginning of script execution.

    import cv2
    import numpy as np

    capture = cv2.VideoCapture(1)
    codec = cv2.VideoWriter_fourcc(*'XVID')
    output = cv2.VideoWriter('CAPTURE.avi', codec, 30, (640, 480))

    while True:
        ret, frame_temp = capture.read()
        cv2.imshow('FRAME', frame_temp)
        key=cv2.waitKey(1)
        if key%256 == 27:
            break
        elif key%256 == 32:
            output.write(frame_temp)

    capture.release()
    output.release()
    cv2.destroyAllWindows()

So, instead when the program runs I would like;

• Program runs and shows the live stream.
• Begin recording the stream when SPACE is hit and stop the recording when SPACE is hit once more.

Any suggestions would be much appreciated.

Answer 1

You need an extra variable to figure out if you are recording. I made a variable called recording_flag

import cv2
import numpy as np

capture = cv2.VideoCapture(1)
codec = cv2.VideoWriter_fourcc(*'XVID')

recording_flag = False

while True:
    ret, frame_temp = capture.read()
    cv2.imshow('FRAME', frame_temp)
    key=cv2.waitKey(1)
    if key%256 == 27:
        break
    elif key%256 == 32:
        if recording_flag == False:
            # we are transitioning from not recording to recording
            output = cv2.VideoWriter('CAPTURE.avi', codec, 30, (640, 480))
            recording_flag = True
        else:
            # transitioning from recording to not recording
            recording_flag = False

    if recording_flag:
        output.write(frame_temp)

capture.release()
output.release()
cv2.destroyAllWindows()