Question

如何利用opencv 从一段AVI视频中获取每一帧的图像

如何利用opencv，从一段AVI视频中获取每一帧的图像，请附上详细的解释，如果够清楚，追加20分

Answer 1

// 该程序实现视频和图片的相互转换.
// Image_to_video()函数将一组图片合成AVI视频文件.
// Video_to_image()函数将AVI视频文件读入，将每一帧存储为jpg文件.
//
////////////////////////////////////////////////////////////////////////
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <cv.h>
#include <highgui.h>
#define NUM_FRAME 300 //只处理前300帧，根据视频帧数可修改

void Video_to_image(char* filename)
{
printf("------------- video to image ... ----------------\n");
//初始化一个视频文件捕捉器
CvCapture* capture = cvCaptureFromAVI(filename);
//获取视频信息
cvQueryFrame(capture);
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);
printf("\tvideo height : %d\n\tvideo width : %d\n\tfps : %d\n\tframe numbers : %d\n", frameH, frameW, fps, numFrames);
//定义和初始化变量
int i = 0;
IplImage* img = 0;
char image_name[13];

cvNamedWindow( "mainWin", CV_WINDOW_AUTOSIZE );
//读取和显示
while(1)
{

img = cvQueryFrame(capture); //获取一帧图片
cvShowImage( "mainWin", img ); //将其显示
char key = cvWaitKey(20);

sprintf(image_name, "%s%d%s", "image", ++i, ".jpg");//保存的图片名

cvSaveImage( image_name, img); //保存一帧图片

if(i == NUM_FRAME) break;
}
cvReleaseCapture(&capture);
cvDestroyWindow("mainWin");
}

void Image_to_video()
{
int i = 0;
IplImage* img = 0;
char image_name[13];
printf("------------- image to video ... ----------------\n");
//初始化视频编写器，参数根据实际视频文件修改
CvVideoWriter *writer = 0;
int isColor = 1;
int fps = 30; // or 25
int frameW = 400; // 744 for firewire cameras
int frameH = 240; // 480 for firewire cameras
writer=cvCreateVideoWriter("out.avi",CV_FOURCC('X','V','I','D'),fps,cvSize(frameW,frameH),isColor);
printf("\tvideo height : %d\n\tvideo width : %d\n\tfps : %d\n", frameH, frameW, fps);
//创建窗口
cvNamedWindow( "mainWin", CV_WINDOW_AUTOSIZE );
while(i<NUM_FRAME)
{
sprintf(image_name, "%s%d%s", "image", ++i, ".jpg");
img = cvLoadImage(image_name);
if(!img)
{
printf("Could not load image file...\n");
exit(0);
}
cvShowImage("mainWin", img);
char key = cvWaitKey(20);
cvWriteFrame(writer, img);
}
cvReleaseVideoWriter(&writer);
cvDestroyWindow("mainWin");
}

int main(int argc, char *argv[])
{
char filename[13] = "infile.avi";
Video_to_image(filename); //视频转图片
Image_to_video(); //图片转视频
return 0;
}
//---------------------------------------------------