如何在OpenCV 3.1.0中设置摄像头编解码器？

import cv2

cap = cv2.VideoCapture(0)

if not cap.isOpened():
    print("无法打开摄像头")
    exit()

fourcc = cv2.VideoWriter_fourcc(*'XVID')

cap.set(cv2.CAP_PROP_FOURCC, fourcc)

cap.release()

import cv2

cap = cv2.VideoCapture(0)

if not cap.isOpened():
    print("无法打开摄像头")
    exit()

fourcc = cv2.VideoWriter_fourcc(*'XVID')
cap.set(cv2.CAP_PROP_FOURCC, fourcc)

cap.release()