python 处理视频输入输出

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()