python opencv 摄像头 视频处理

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# 从摄像头捕捉
import numpy as np
import cv2
cap = cv2.VideoCapture(0)
while(True):
    ret, frame = cap.read()
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
cap.release()
cv2.destroyAllWindows()

# 处理视频
import numpy as np
import cv2
cap = cv2.VideoCapture('video.mp4')
while(cap.isOpened()):
    ret,frame = cap.read();
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    cv2.imshow('frame',gray)
    if cv2.waitKey(1)==ord('q'):
        break;
cap.release()
cv2.destroyAllWindows()

# 下面的代码从摄像头捕获视频，每一帧都垂直翻转，然后保存
# 转码失败


import numpy as np
import cv2
cap = cv2.VideoCapture('video.avi')
fourcc = cv2.VideoWriter_fourcc('P', 'I', 'M', 'I')
out = cv2.VideoWriter('turn_video.avi',fourcc, 20.0, (640, 480))
while(cap.isOpened()):
    ret,frame = cap.read()
    if ret == True:
        frame = cv2.flip(frame, 0)
        out.write(frame)
        cv2.imshow('frame', frame)
        if cv2.waitKey(1) == ord('q'):
            break
        else:
            break

# Release everything if job is finished
cap.release()
out.release()
cv2.destroyAllWindows()