Video to image -cv2 Videocapture() usage

purpose ： Video frame extraction , Video visualization
1、cap = cv2.VideoCapture(0)
VideoCapture() Parameter is 0, Indicates that the built-in camera of the notebook is turned on , If the parameter is the path of the video file, open
Such as cap = cv2.VideoCapture(“…/test.avi”)

#  If the parameter is the path of the video file, open 
cap = cv2.VideoCapture('./RobustPCA_video_demo.avi')

2、ret,frame = cap.read()
cap.read() Read video by frame ,ret,frame Yes cap.read() Method .
among ret Boolean value , If the read frame is correct, return True, If the file reads to the end , Its return value is False.
frame It's the image of every frame , It's a three-dimensional matrix .
3、 cv2.destroyAllWindows() To delete a window ,（） No parameters are specified in the , Delete all windows , Delete a specific window , Go to （） Enter a specific window value .

4、 call release() Release camera , call destroyAllWindows() Close all image windows .

import cv2
# cv2.VideoCapture  Video frame extraction , Video visualization 
#  If the parameter is the path of the video file, open 
cap = cv2.VideoCapture('./RobustPCA_video_demo.avi')
all_frames = []
while(cap.isOpened()):
	# ret Boolean value , If the read frame returns correctly true, When reading to the end, it will return false
	# frame Is the image of each frame , It's a three-dimensional matrix 
    ret, frame = cap.read()
    if not ret :
        break
    all_frames.append(frame)
cap.release()
cv2.destroyAllWindows()

cv2.VideoCapture() Usage and examples
cv2.waitKey() and cv2.destroyAllWindows()