如何用python获取视频文件播放时长？cv2 opencv

除了moviepy还可以用opencv。跑起来比moviepy快多了。

def get_video_duration(filename):
  cap = cv2.VideoCapture(filename)
  if cap.isOpened():
    rate = cap.get(5)
    frame_num =cap.get(7)
    duration = frame_num/rate
    return duration
  return -1