OpenCV study notes: video processing

Environment : CentOS7
g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16)

$ pkg-config --modversion opencv
2.4.13

The video used in the test is the avi test video that comes with Opencv. The file path is: opencv-3.4.0\sources\samples\data\vtest.avi

If you can't find the download, you can also go to https://download.csdn.net/download/rong_toa/10392225 to download.

Source code:

#include<stdlib.h>
#include<stdio.h>
#include<math.h>
#include<cv.h>
#include<highgui.h>
#include<iostream>
using namespace std;

int main(int argc,char**argv)
{
/******Initialize a camera capture******/
    //CvCapture* capture1 = cvCaptureFromCAM(0);

/*****Initialize a video file capturer*****/
    CvCapture* capture = cvCaptureFromAVI("vtest.avi");
    /**/
    IplImage* img = 0;
    if(!cvGrabFrame(capture)){ // capture a frame
        printf("Could not grab a frame\n\7");
        exit(0);
    }
    img=cvRetrieveFrame(capture);
    cvSaveImage("out.jpg",img);

/******Get/Set video stream information*****/
    /*Get video streaming device information*/
    cvQueryFrame(capture); // Do this before reading the video stream information
    int frameH = (int) cvGetCaptureProperty(capture, CV_CAP_PROP_FRAME_HEIGHT);
    int frameW = (int) cvGetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH);
    int fps = (int) cvGetCaptureProperty(capture, CV_CAP_PROP_FPS);
    int numFrames = (int) cvGetCaptureProperty(capture, CV_CAP_PROP_FRAME_COUNT);
    /*Get frame info*/
    float posMsec = cvGetCaptureProperty(capture, CV_CAP_PROP_POS_MSEC);
    int posFrames = (int) cvGetCaptureProperty(capture, CV_CAP_PROP_POS_FRAMES);
    float posRatio = cvGetCaptureProperty(capture, CV_CAP_PROP_POS_AVI_RATIO);
    /*Set the position of the first frame captured from the video file*/
    //cvSetCaptureProperty(capture, CV_CAP_PROP_POS_AVI_RATIO, (double)0.9);
    img=cvRetrieveFrame(capture);
    cvSaveImage("out2.jpg",img);

/******Save video file******/
    /* Initialize the video writer */
    CvVideoWriter *writer = 0;
    int isColor = 1;
    //fps = 25; // or 30
    //frameW = 640; // 744 for firewire cameras
    //frameH = 480; // 480 for firewire cameras
    writer=cvCreateVideoWriter("out.avi",CV_FOURCC('D', 'I', 'V', 'X'),
                                fps,cvSize(frameW,frameH),isColor);
    /*Save the video file*/
    IplImage* img1 = 0;
    int nFrames = 80, key;
    for(int i=0;i<nFrames;i++){
        cvGrabFrame(capture); // capture a frame
        img1=cvRetrieveFrame(capture); // retrieve the captured frame
        // img = cvQueryFrame(capture);
        cvShowImage("mainWin", img);
        key=cvWaitKey(40); // wait 20 ms
        cvWriteFrame(writer,img1); // add the frame to the file
    }
    /* release the video stream catcher */
    cvReleaseCapture(&capture);
    /* release the video writer */
    cvReleaseVideoWriter(&writer);
    return 0;
}

Compile and run:

$ make
g++ main.cpp `pkg-config --cflags --libs opencv`
$ ./a.out

After running, a window will pop up to play a video, and two video screenshots will be saved after running (an example is given here).

For more information, see: "OpenCV Chinese Reference Manual"