[Python] Opencv saving empty video Python

I am facing a problem in recording a video from camera. I am using python and opencv to do so. I have my images in QImage format, I convert them to numpy array in order to display to stream it when video capturing of the cam (using VideoCapture of opencv), everything works fine.
When I try to record a video and save it in the folder (using VideoWriter_fourcc of opencv), I get no errors but I get an empty video. I did a lot of searching to find the problem but I couldn't.

Here's the code that I use to record a video:

import cv2

fourcc = cv2.VideoWriter_fourcc('M','J','P','G')
#img is a numpy array
videoWriter = cv2.VideoWriter('video.avi', fourcc, 20, (img.shape[0],img.shape[1]))
while True:
videoWriter.write(img)
videoWriter.release()


I tried to change the Framerate, the frameSize, the extension of the video and the code of codec but nothing worked.

Any suggestion ?

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