Small sample code that uses OpenCV to show images from a camera. If an mp.Manager is created, the code stops working. Commenting the line fixes it but why???

opencv-multiprocessing-issue

import cv2
import multiprocessing as mp

cap = cv2.VideoCapture(0)

manager = mp.Manager()  # Comment this line to make the code work

with mp.Lock():
    cap.set(6, cv2.VideoWriter_fourcc(*list('MJPG')))

ESC = 27
while(True):
    ret, frame = cap.read()
    cv2.imshow('frame', frame)
    if cv2.waitKey(1) & 0xFF == ESC:
        break

cap.release()
cv2.destroyAllWindows()