OpenCV saving video to file

问题:

I think my question is pretty basic, but I'm writing this code in OpenCV to simply capture video data from the webcam and save it to file. Now the problem is that the file gets made at the desired destination, it initially is about 286 bytes in size. Then when I assign the first frame to the pointer, the size increases to 414 bytes. However, when I run the whole code, the size of the saved video remains 414 bytes. Of course, as a result my media player cannot play the file and says " is not in a format that QuickTime Player understands." and the same happens with the VLC player.

Here is my code for the same:

#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>

int main( int argc, char** argv ) {
CvCapture* capture;

capture = cvCreateCameraCapture(0);

assert( capture != NULL );

IplImage* bgr_frame = cvQueryFrame( capture );

CvSize size = cvSize(
                     (int)cvGetCaptureProperty( capture,
                                               CV_CAP_PROP_FRAME_WIDTH),
                     (int)cvGetCaptureProperty( capture,
                                               CV_CAP_PROP_FRAME_HEIGHT)
                     );

cvNamedWindow( "Webcam", CV_WINDOW_AUTOSIZE );

CvVideoWriter *writer = cvCreateVideoWriter(    "/Users/user/Desktop/OpenCV_trial/OpenCV_trial/vidtry.AVI",
                                            CV_FOURCC('D','I','V','X'),
                                            30,
                                            size
                                            );

while( (bgr_frame = cvQueryFrame( capture )) != NULL ) 
{
    cvWriteFrame(writer, bgr_frame );
    cvShowImage( "Webcam", bgr_frame );
    char c = cvWaitKey( 33 );
    if( c == 27 ) break;
}
cvReleaseVideoWriter( &writer );
cvReleaseCapture( &capture );
cvDestroyWindow( "Webcam" );
return( 0 );
}

I don't know why this is happening. I am using the mac OSX Lion and running Xcode.

Has anyone faced this problem before? If so, how could I solve it?

Thank you!

-Yash

回答1:

Have you try to open your file with another player? VLC for instance..

This because Quicktime and .avi do not get along very well.

Take a look on apple documentation.

Otherwise try to change the video codec, this is the opencv reference.

回答2:

Hi I think I found the answer to the question.

As Velthune had suggested, it seems to be a codec issue and the MAC OS can run only a few of them. Here is the link for all the ones that work: List of QuickTime codecs supported by the mac os port

Not all of the codecs listed there work though. Out of all the ones that I tried only the WRLE seemed to work.

Thanks a lot Velthune. -Yash

回答3:

Actually I too was trying to do same. But its that i tried in Visual C++ (Express Edition) in windows 7. But in this case we need to add extra header as "#include "stdafx.h" and also make sure the link to save the file exists. For example the code i modified was as:

#include "stdafx.h"
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>

int main( int argc, char** argv ) {
CvCapture* capture;

capture = cvCreateCameraCapture(0);

assert( capture != NULL );

IplImage* bgr_frame = cvQueryFrame( capture );

CvSize size = cvSize(
                     (int)cvGetCaptureProperty( capture,
                                               CV_CAP_PROP_FRAME_WIDTH),
                     (int)cvGetCaptureProperty( capture,
                                               CV_CAP_PROP_FRAME_HEIGHT)
                     );

cvNamedWindow( "Webcam", CV_WINDOW_AUTOSIZE );

CvVideoWriter *writer = cvCreateVideoWriter("D:/vidtry.AVI",CV_FOURCC('D','I','V','X'),15,size);

while( (bgr_frame = cvQueryFrame( capture )) != NULL ) 
{
    cvWriteFrame(writer, bgr_frame );
    cvShowImage( "Webcam", bgr_frame );
    char c = cvWaitKey( 33 );
    if( c == 27 ) break;
}
cvReleaseVideoWriter( &writer );
cvReleaseCapture( &capture );
cvDestroyWindow( "Webcam" );
return( 0 );
}