Python openCV video recording not in true time-CodePudding

Trying to record "time true" video with openCV. When recording video footage it seems to be slightly sped up. If I hold a timer up to the webcam and then play it back saved footage is 3 - 5 seconds too fast per minute of saved footage.

How can I get the saved video to be exactly 1 minute if I record 1 minute from my webcam? Or 2 minutes of recording to be an exported 2-minute video?

import cv2
 
cap = cv2.VideoCapture(0)

fps = cap.get(cv2.CAP_PROP_FPS)
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 640)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 480)

width  = cap.get(cv2.CAP_PROP_FRAME_WIDTH)   # float `width`
height = cap.get(cv2.CAP_PROP_FRAME_HEIGHT)  # float `height`

fourcc = cv2.VideoWriter_fourcc(*'XVID')
videoWriter = cv2.VideoWriter('MYPATH\\video.avi', fourcc, fps, (int(width),int(height)))
 
while (True):
    ret, frame = cap.read()
    if ret:
        cv2.imshow('video', frame)
        videoWriter.write(frame)
 
    if cv2.waitKey(1) == 27:
        break
 
cap.release()
videoWriter.release()
cv2.destroyAllWindows()

CodePudding user response：

Your program may write additional frames because True sentence at line 16 in your while loop, then change that value to check as conditional ret, by:

...
ret, frame = cap.read()
while (ret):    
    cv2.imshow('video', frame)
    videoWriter.write(frame)
 
    ret, frame = cap.read()

    if cv2.waitKey(1) == 27:
        break

cap.release()
videoWriter.release()
cv2.destroyAllWindows()

CodePudding user response：

I have no idea why this fixed it... but changing the forcc to fourcc = cv2.VideoWriter_fourcc(*'MP4V') and then changing the output file from .avi to .mp4 fixed the problem.