1. OpenvCV讀/寫視訊檔案

import cv2

videoCapture = cv2.VideoCapture('MyInputVid.avi')
fps = videoCapture.get(cv2.cv.CV_CAP_PROP_FPS)
size = (int(videoCapture.get(cv2.cv.CV_CAP_PROP_FRAME_WIDTH)), int(videoCapture.get(cv2.cv.CV_CAP_PROP_FRAME_HEIGHT)))
videoWriter = cv2.VideoWriter('MyOutputVid.avi', cv2.cv.CV_FOURCC('I', '4', '2', '0'), fps, size)  #YUV編碼格式

success, frame = videoCapture.read()
while success: # Loop until there are no more frames.
    videoWriter.write(frame)
    success, frame = videoCapture.read()

 

寫視訊檔案時可用的編碼格式如下：

cv2.cv.CV_FOURCC('I','4','2','0') : YUV 4:2:0(.avi)
cv2.cv.CV_FOURCC('P','I','M','1') : MPEG-1(.avi)
cv2.cv.CV_FOURCC('M','J','P','G') : motion-JPEG(.avi)
cv2.cv.CV_FOURCC('T','H','E','O') : Ogg-Vorbis(.ogv)
cv2.cv.CV_FOURCC('F','L','V','1') : Flash video(.flv)

 2. 捕獲視訊幀

import cv2

cameraCapture = cv2.VideoCapture(0)
fps = 30 # an assumption
size = (int(cameraCapture.get(cv2.cv.CV_CAP_PROP_FRAME_WIDTH)), int(cameraCapture.get(cv2.cv.CV_CAP_PROP_FRAME_HEIGHT)))
videoWriter = cv2.VideoWriter('MyOutputVid.avi', cv2.cv.CV_FOURCC('I','4','2','0'), fps, size)

success, frame = cameraCapture.read()
numFramesRemaining = 10 * fps - 1
while success and numFramesRemaining > 0:
    videoWriter.write(frame)
    success, frame = cameraCapture.read()
    numFramesRemanining -= 1
 

 videoCapture.get()方法往往獲取不到正確的fps，這裡給定一個估計值。

若讀取不到視訊幀時會返回（false， None）。

read（）方法對獲取一組攝像機的視訊幀時使用不夠恰當，需要使用grab()和retrieve()方法代替。

success0 = cameraCapture0.grab()
success1 = cameraCapture1.grab()
if success0 and success1:
    frame0 = cameraCapture0.retrieve()
    frame1 = cameraCapture1.retrieve()

對於一個多路攝像機，需要在retrieve()中指明每路的index：

success = multiHeadCameraCapture.grab()
if success:
    frame0 = multiHeadCameraCapture.retrieve(channel = 0)
    frame1 = multiHeadCameraCapture.retrieve(channel = 1)

3.在視窗中顯示視訊幀

import cv2

clicked = False
def onMouse(event, x, y, flags, param):
    global clicked
    if event == cv2.cv.CV_EVENT_LBUTTONUP:
        click = True

cameraCapture = cv2.VideoCapture(0)
cv2.namedWindow('MyWindow')
cv2.setMouseCallback('MyWindow', onMouse)

print 'Showing camera feeed. Click window or press any key to stop.'
success, frame = cameraCapture.read()
while success and cv2.waitKey(1) == -1 and not clicked:
    cv2.imshow('MyWindow', frame)
    success, frame = cameraCapture.read()

cv2.destroyWindow('MyWindow')

Python提供一個標準函式ord()將字元轉換為ASCII碼，ord('a') = 97