python opencv显示rtsp视频

import cv2
print("ok1")
cap = cv2.VideoCapture("http://clips.vorwaerts-gmbh.de/big_buck_bunny.mp4")
print("ok2")
ret,frame = cap.read()
if ret==1:
    print("ok")
else:
    print("error")
while ret:
    ret,frame = cap.read()
    cv2.imshow("frame",frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
cv2.destroyAllWindows()
cap.release()