用OpenCV播放视频

Question

我是OpenCV的初学者，我希望在OpenCV中播放视频。我做了一个代码，但它只显示一个图像。我使用的是OpenCV 2.1和Visual Studio 2008。如果有人指引我哪里走错了，我会非常感激。下面是我粘贴的代码:

#include "stdafx.h"
#include "cv.h"
#include "highgui.h"
int main()
{
CvCapture* capture = cvCaptureFromAVI("C:/OpenCV2.1/samples/c/tree.avi");
IplImage* img = 0; 
if(!cvGrabFrame(capture)){              // capture a frame 
printf("Could not grab a framen7");
exit(0);}
cvQueryFrame(capture); // this call is necessary to get correct 
                   // capture properties
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);
///numFrames=total number of frames

printf("Number of rows %dn",frameH);
printf("Number of columns %dn",frameW,"n");
printf("frames per second %dn",fps,"n");
printf("Number of frames %dn",numFrames,"n");
for(int i=0;i<numFrames;i++)
{
IplImage* img = 0;
img=cvRetrieveFrame(capture); 
cvNamedWindow( "img" );
cvShowImage("img", img);
}
cvWaitKey(0);
cvDestroyWindow( "img" );
cvReleaseImage( &img );
cvReleaseCapture(&capture);

return 0;
}

Answer 1

您必须使用cvQueryFrame而不是cvRetrieveFrame。正如@Chipmunk指出的那样，你必须在cvShowImage之后添加延迟。

#include "stdafx.h" 
#include "cv.h"       
#include "highgui.h"
cvNamedWindow( "img" );
for(int i=0;i<numFrames;i++)
{
   IplImage* img = cvQueryFrame(capture); 
   cvShowImage("img", img);
   cvWaitKey(10);
}

下面是使用OpenCV播放视频的完整方法:

int main()
{
    CvCapture* capture = cvCreateFileCapture("C:/OpenCV2.1/samples/c/tree.avi");
    IplImage* frame = NULL;
    if(!capture)
    {
        printf("Video Not Openedn");
        return -1;
    }
    int width = (int)cvGetCaptureProperty(capture,CV_CAP_PROP_FRAME_WIDTH);
    int height = (int)cvGetCaptureProperty(capture,CV_CAP_PROP_FRAME_HEIGHT);
    double fps = cvGetCaptureProperty(capture, CV_CAP_PROP_FPS);
    int frame_count = (int)cvGetCaptureProperty(capture,  CV_CAP_PROP_FRAME_COUNT);
    printf("Video Size = %d x %dn",width,height);
    printf("FPS = %fnTotal Frames = %dn",fps,frame_count);
    while(1)
    {
        frame = cvQueryFrame(capture);
        if(!frame)
        {
            printf("Capture Finishedn");
            break;
        }
        cvShowImage("video",frame);
        cvWaitKey(10);
    }
    cvReleaseCapture(&capture);
    return 0;
}

Answer 2

在窗口上显示图像后，必须延迟或等待下一个图像才能显示，我想你可以猜到为什么会这样。对于延迟，我们用cvWaitKey()。这就是我在循环代码中添加的内容。

cvNamedWindow( "img" );
for(int i=0;i<numFrames;i++)
{
   IplImage* img = 0;
   img=cvRetrieveFrame(capture); 
   cvShowImage("img", img);
   cvWaitKey(10); 
}