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Python-OpenCV 处理视频（一）：输入输出

视频的处理和图片的处理类似，只不过视频处理需要连续处理一系列图片。

一般有两种视频源，一种是直接从硬盘加载视频，另一种是获取摄像头视频。

0x00. 本地读取视频

核心函数:

cv.CaptureFromFile()

代码示例：

import cv2.cv as cv  capture = cv.CaptureFromFile('myvideo.avi')  nbFrames = int(cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FRAME_COUNT))  #CV_CAP_PROP_FRAME_WIDTH Width of the frames in the video stream #CV_CAP_PROP_FRAME_HEIGHT Height of the frames in the video stream  fps = cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FPS)  wait = int(1/fps * 1000/1)  duration = (nbFrames * fps) / 1000  print 'Num. Frames = ', nbFrames print 'Frame Rate = ', fps, 'fps' print 'Duration = ', duration, 'sec'  for f in xrange( nbFrames ):     frameImg = cv.QueryFrame(capture)     print cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_POS_FRAMES)     cv.ShowImage("The Video", frameImg)     cv.WaitKey(wait)

cv2

import numpy as np import cv2 cap = cv2.VideoCapture('vtest.avi') while(cap.isOpened()):  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()

0x01. 摄像头视频读取

核心函数：

cv.CaptureFromCAM()

示例代码：

import cv2.cv as cv capture = cv.CaptureFromCAM(0) while True:  frame = cv.QueryFrame(capture)  cv.ShowImage("Webcam", frame)  c = cv.WaitKey(1)  if c == 27: #Esc on Windows   break

cv2

import numpy as np import cv2 cap = cv2.VideoCapture(0) while(True):  # Capture frame-by-frame  ret, frame = cap.read()  # Our operations on the frame come here  gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)  # Display the resulting frame  cv2.imshow('frame',gray)  if cv2.waitKey(1) & 0xFF == ord('q'):   break # When everything done, release the capture cap.release() cv2.destroyAllWindows()

0x02. 写入视频

摄像头录制视频

import cv2.cv as cv capture=cv.CaptureFromCAM(0) temp=cv.QueryFrame(capture) writer=cv.CreateVideoWriter("output.avi", cv.CV_FOURCC("D", "I", "B", " "), 5, cv.GetSize(temp), 1) #On linux I used to take "M","J","P","G" as fourcc count=0 while count<50:  print count  image=cv.QueryFrame(capture)  cv.WriteFrame(writer, image)  cv.ShowImage('Image_Window',image)  cv.WaitKey(1)  count+=1

从文件中读取视频并保存

import cv2.cv as cv capture = cv.CaptureFromFile('img/mic.avi')  nbFrames = int(cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FRAME_COUNT)) width = int(cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FRAME_WIDTH)) height = int(cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FRAME_HEIGHT)) fps = cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FPS) codec = cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FOURCC)  wait = int(1/fps * 1000/1) #Compute the time to wait between each frame query  duration = (nbFrames * fps) / 1000 #Compute duration  print 'Num. Frames = ', nbFrames print 'Frame Rate = ', fps, 'fps'  writer=cv.CreateVideoWriter("img/new.avi", int(codec), int(fps), (width,height), 1) #Create writer with same parameters  cv.SetCaptureProperty(capture, cv.CV_CAP_PROP_POS_FRAMES,80) #Set the number of frames  for f in xrange( nbFrames - 80 ): #Just recorded the 80 first frames of the video      frame = cv.QueryFrame(capture)      print cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_POS_FRAMES)      cv.WriteFrame(writer, frame)      cv.WaitKey(wait)

cv2

import numpy as np import cv2 cap = cv2.VideoCapture(0) # Define the codec and create VideoWriter object fourcc = cv2.VideoWriter_fourcc(*'XVID') out = cv2.VideoWriter('output.avi',fourcc, 20.0, (640,480)) while(cap.isOpened()):  ret, frame = cap.read()  if ret==True:   frame = cv2.flip(frame,0)   # write the flipped frame   out.write(frame)   cv2.imshow('frame',frame)   if cv2.waitKey(1) & 0xFF == ord('q'):    break  else:   break # Release everything if job is finished cap.release() out.release() cv2.destroyAllWindows()

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