opencv-python调用摄像头

import cv2import numpy as npcap = cv2.VideoCapture(0)fourcc = cv2.cv.CV_FOURCC(*'XVID')#opencv3的话用:fourcc = cv2.VideoWriter_fourcc(*'XVID')out = cv2.VideoWriter('output.avi',fourcc,20.0,(640,480))#保存视频while True:    ret,frame = cap.read()    gray = cv2.cvtColor(frame,cv2.COLOR_BGR2GRAY)    out.write(frame)#写入视频    cv2.imshow('frame',frame)        if cv2.waitKey(1) &0xFF == ord('q'):        breakcap.release()out.release()cv2.destroyAllWindows()