Writing AVI files in OpenCV

There example on the net and code given in Learn OpenCv,Orielly.

After many attempts the out.avi file is written with 0 bytes. I wonder where i went wrong.

The following are the code i used...

int main(int argc, char* argv[]) {
    CvCapture* input = cvCaptureFromFile(argv[1]);
    IplImage* image = cvRetrieveFrame(input);

    if (!image) {
        printf("Unable to read input");
        return 0;
    }


    CvSize imgSize;
    imgSize.width = image->width;
    imgSize.height = image->height;



    double fps = cvGetCaptureProperty(
            input,
            CV_CAP_PROP_FPS
            );

    CvVideoWriter *writer = cvCreateVideoWriter(
            "out.avi",
            CV_FOURCC('M', 'J', 'P', 'G'),
            fps,
            imgSize
            );


    IplImage* colourImage;
    //Keep processing frames...
    for (;;) {

        //Get a frame from the input video.
        colourImage = cvQueryFrame(input);
        cvWriteFrame(writer, colourImage);

    }

    cvReleaseVideoWriter(&writer);
    cvReleaseCapture(&input);

}

From stackoverflow

• Maybe you could try inserting a printf("Frame found\n") inside the for(;;) to see if it is actually capturing frames. Or even better:

  if(colourImage == NULL) {
      printf("Warning - got NULL colourImage\n");
      continue;
  }
  cvNamedWindow( "test", 1);
  cvShowImage( "test", colourImage );
  cvWaitKey( 0 );
  cvDestroyWindow( "test" );
  

  Then see if you get any windows, and if they contain the right contents.

• My bet is that cvCreateVideoWriter returns NULL. Just step through it to see if it's true. In that case, the problem is probably with CV_FOURCC(..) which doesnt find the codec and force a return 0;

  you can try using -1 instead of CV_FOURCC. There is gonna be a prompt during runtime for you to chose the appropriate codec

  : Thanks Eric you are right

• I've a problem under MacOs 10.4. When I try to execute this row

  CvVideoWriter *writer = cvCreateVideoWriter(
              "out.avi",
              CV_FOURCC('M', 'J', 'P', 'G'),
              fps,
              imgSize
              );
  

  i've this problem:

  OpenCV ERROR: Internal error (Cannot create data reference from file name) in function icvCreateVideoWriter, cvcap_qt.cpp(1291) Terminating the application...

  any idea?

  Eric : if you have another problem please make a separate question

• When i google this problem i meet an answer: "OpenCV on mac os x don`t support avi write until it will be compiled with a ffmpeg"

  For me seem to wrok this solution http://article.gmane.org/gmane.comp.lib.opencv/16005

  You need to provide the full path to the file with the movie in cvCreateVideoWriter. I don't know whether it's only an Mac OS X port issue, but might be, since QTNewDataReferenceFromFullPathCFString from the QT backend is used.

• Friends I faced the same problem; the methods suggested by Eric does work. The problem, i think lies with the availability of the codecs. Thanks to all of you....

• Hi ,

  I have the following code , and NONE of the functions are returning NULL, so I guess everything is proper.

  But still the file size of the test.avi file is 0 bytes

          CvCapture *pCapturedImage = cvCreateCameraCapture(0); // get the default camera, for me it is a webcam
  

  // Get the avi file name CString strFileName = objFileDlg.GetPathName()+".avi"; // test.avi

          int isColor = 1;
          int fps     = 25;  // or 30
          int frameW  = 640; // 744 for firewire cameras
          int frameH  = 480; // 480 for firewire cameras
          CvVideoWriter *pVideoWriter = cvCreateVideoWriter(strFileName.GetBuffer(),
  

  -1, // I am choosing the uncompressed format** fps,cvSize(frameW,frameH),isColor);

  // pVideoWriter does not return NULL , that means its succesful

          cvNamedWindow("mainWin",CV_WINDOW_AUTOSIZE);
          IplImage *pImage = 0;
  
          int nFrames = 50;
          for(int i=0;i<nFrames;i++)
          {
                cvGrabFrame(pCapturedImage);          // capture a frame
                pImage=cvRetrieveFrame(pCapturedImage);  // retrieve the captured frame
                cvWriteFrame(pVideoWriter,pImage);      // add the frame to the file
  
                cvShowImage("mainWin",pImage);     // NO IMAGE SHOWS UP
                cvWaitKey(20);
  
          }
  
          cvDestroyWindow("mainWin");
          cvReleaseVideoWriter(&pVideoWriter);
  

  Please let me know what am I missing out.

  Thanks, Sujay

• hey This code works in DevC++ try it:

    #include<cv.h>
    #include<highgui.h>
    #include<cvaux.h>
    #include<cvcam.h>
    #include<cxcore.h>
  
    int main()
    {
    CvVideoWriter *writer = 0;
    int isColor = 1;
    int fps     = 5;  // or 30
    int frameW  = 1600; //640; // 744 for firewire cameras
    int frameH  = 1200; //480; // 480 for firewire cameras
    //writer=cvCreateVideoWriter("out.avi",CV_FOURCC('P','I','M','1'),
    //                           fps,cvSize(frameW,frameH),isColor);
    writer=cvCreateVideoWriter("out.avi",-1,
                         fps,cvSize(frameW,frameH),isColor);
    IplImage* img = 0; 
  
    img=cvLoadImage("CapturedFrame_0.jpg");
    cvWriteFrame(writer,img);      // add the frame to the file
    img=cvLoadImage("CapturedFrame_1.jpg");
    cvWriteFrame(writer,img);
    img=cvLoadImage("CapturedFrame_2.jpg");
    cvWriteFrame(writer,img);
    img=cvLoadImage("CapturedFrame_3.jpg");
    cvWriteFrame(writer,img);
    img=cvLoadImage("CapturedFrame_4.jpg");
    cvWriteFrame(writer,img);
    img=cvLoadImage("CapturedFrame_5.jpg");
    cvWriteFrame(writer,img);
  
    cvReleaseVideoWriter(&writer);
    return 0;
    }
  

  I compiled it and ran it, works fine. (I did not see above whether you got your answer or not .. but for this particular thing I worked very hard earlier and suddenly I just did it, from some code snippets.)

• This code worked fine:

  cv.h highgui.h cvaux.h cvcam.h cxcore.h

  int main(){

  CvVideoWriter *writer = 0;
  int isColor = 1;
  int fps     = 5;  // or 30
  IplImage* img = 0; 
  img=cvLoadImage("animTest_1.bmp");
  int frameW  = img->width; //640; // 744 for firewire cameras
  int frameH  = img->height; //480; // 480 for firewire cameras
  
  writer=cvCreateVideoWriter("out.avi",-1,
   fps,cvSize(frameW,frameH),1);
  
  cvWriteFrame(writer, img);      // add the frame to the file
  
  char *FirstFile,fF[20]="",*fileNoStr,fns[4]="";
  fileNoStr=fns;
  for(int fileNo;fileNo<100;fileNo++){
   FirstFile=fF;   
   itoa(fileNo,fileNoStr,10);
   FirstFile=strcat ( FirstFile,"animTest_");
   FirstFile=strcat ( FirstFile,fileNoStr);
   FirstFile=strcat ( FirstFile,".bmp");
  
   printf(" \n%s .",FirstFile);
   img=cvLoadImage(FirstFile);
  
   cvWriteFrame(writer, img);
  
  }
  cvReleaseVideoWriter(&writer);
  
  return 0;
  

  }

• I think the problem you're encountering is that your "for" loop never ends; therefore, "cvReleaseVideoWriter(&writer);" and "cvReleaseCapture(&input);" never get called. Try something like "for(int i=0; i<200; i++)" and see if you end up with a working video.

  Often video is written to a temporary files before being finalized on disk. If your file isn't finalized, there won't be anything to see.

  Hope that helps.