Writing AVI files in OpenCV

Question

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);

}

Answer 1

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.

Answer 2

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

Answer 3

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?

Answer 4

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.

Answer 5

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....

Answer 6

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

Answer 7

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.)

Answer 8

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;

}

Answer 9

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.