如何从视频保存下一个和当前帧

Question

我想从相同视频的previous帧中减去current帧的视频，并对所有视频和write those frame as seprate video做同样的事情，我很困惑保存当前帧和下一帧。如何保存它们，以便在下一帧到来之成为以前的下一帧

IplImage* skipNFrames(CvCapture* capture, int n) 
{ 

    for(int i = 0; i < n; ++i) 
    { 
     if(cvQueryFrame(capture) == NULL) 
     { 
      return NULL; 
     } 
    else 
    { 

     char* New_image; 
    // New_image* = cvQueryFrame(capture) - cvCloneImage(capture); 
Mat current_frame; 
Mat previous_frame; 

if (!capture.isOpened()) { 
    return -1; 
} 

while(1) 
{ 
    capture >> current_frame; 
    if (current_frame.empty()) 
     break; 
    // do video processing 

    imshow("Window", current_frame); 
    waitKey(10); 
    frame = skipNFrames(capture, 1) 
    frame.copyTo(previous_frame); 

     int frame_width=(int) cvGetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH);  
     int frame_height=(int) cvGetCaptureProperty(capture, CV_CAP_PROP_FRAME_HEIGHT); 
     int fps = (int)cvGetCaptureProperty(capture, CV_CAP_PROP_FPS); 
    //creating video writer structure 
    CvVideoWriter *writer = 0; 
    writer=cvCreateVideoWriter("savedVideo.avi",CV_FOURCC('M', 'P', '4', '2'),fps,cvSize(frame_width,frame_height),1); 

    if(!writer) { 
    //release memory 
     cvReleaseCapture(&capture); 
     return 0; 
     } 

    while(true) { 
      //grab and retrieve each frames of the video sequentially 
      IplImage* frame = cvQueryFrame(New_image); 
      if(!frame) break; 

     //writing frame by frame to the output file 
     cvWriteFrame(writer,frame); 
    } 


    cvReleaseVideoWriter(&writer); 
    cvReleaseCapture(&capture); 

    return 0; 
} 

    } 
    // return cvNew_image  
    //return cvQueryFrame(capture); 
} 
int main(int argc, char* argv[]) 
{ 
    CvCapture* capture = cvCaptureFromFile("try.avi"); 
    char buffer[1000]; 
    int flag=0; 
    IplImage* frame = NULL; 
    do 
    { 
     //frame = skipNFrames(capture, 1); 
     cvNamedWindow("frame", CV_WINDOW_AUTOSIZE); 
     cvShowImage("frame", frame); 
     cvWaitKey(0); 
     char *str=new char[50]; 
     flag++; 
     sprintf(str,"%d",flag); 
     strcat(str," frame"); 
     strcat(str,".png"); 
     Mat image=frame; 
     imwrite(str,image); 
    } while(frame != NULL); 

    cvReleaseCapture(&capture); 
    cvDestroyWindow("frame"); 
    cvReleaseImage(&frame); 

    return 0; 
} 

Answer 1

下面是使用新的OpenCV 2.x的界面例子。此外，在您的代码中，您同时使用IplImage和Mat。在一般情况下，使用的OpenCV的C++接口，除非你有使用C.

VideoCapture cap; 
Mat current_frame; 
Mat previous_frame; 
Mat result;  

cap.open(0); 
if (!cap.isOpened()) { 
    cerr << "can not open camera or video file" << endl; 
    return -1; 
} 

while(1) 
{ 
    cap >> current_frame; 
    if (current_frame.empty()) 
     break; 

    if (! previous_frame.empty()) { 
     // subtract frames 
     subtract(current_frame, previous_frame, result); 
    } 


    imshow("Window", result); 
    waitKey(10); 

    frame.copyTo(previous_frame); 
}