Output Movie in Python cannnot by played

I want to convert a network camera video to grayscale and save it as an another video file. I wrote the following code, but it does not work well. However detect.avi is output, I can not play this file. What is the problem?

rtsp_path = f"rtsp://{userid}:{pwd}@{ip_address}:{rtsp_port}/ipcam_h264.sdp"
video = cv2.VideoCapture(rtsp_path )
savepath = "detect.avi"
frame_Rate = video.get(cv2.CAP_PROP_FPS)
height, width, dim = frame.shape
rec = cv2.VideoWriter(savepath, cv2.VideoWriter_fourcc(*'DIVX'), frame_Rate, (int(width), int(height)))

while (video.isOpened()):

   
 开发者_如何学Python   ret, frame = video.read()
    if frame is None:
        break

    img = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    rec.write(img)

    if cv2.waitKey(30) & 0xFF == ord('q'):
        video.release()
        rec.release()
        cv2.destroyAllWindows()
        break

cv2.destroyAllWindows()
video.release()
rec.release()