Writing AVI files in OpenCV - c

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

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 2

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 3

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 4

It's a codec issue. Try out all the possible codecs (option -1 in cvCreateVideo). In my case Microsoft Video 1 worked well.

Answer 5

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 6

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 7

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.