/* Create an object that decodes the input video stream. */
	CvCapture * input_video = cvCaptureFromFile(
		"optical_flow_input.avi");
	if (input_video == NULL)
	{
		fprintf(stderr, "Error: Can't open video.\n");
		return -1;
	}
 
    CvSize frame_size;
	frame_size.height =
		(int) cvGetCaptureProperty
( input_video, CV_CAP_PROP_FRAME_HEIGHT );
	frame_size.width =
		(int) cvGetCaptureProperty
( input_video, CV_CAP_PROP_FRAME_WIDTH );
 
    	/* Determine the number of frames in the AVI. */
	long number_of_frames;
	/* Go to the end of the AVI (ie: the fraction is "1") */
	cvSetCaptureProperty 
(input_video, CV_CAP_PROP_POS_AVI_RATIO, 1.);
	/* Now that we're at the end, read the AVI position in frames */
	number_of_frames = ( int ) 
cvGetCaptureProperty (input_video, CV_CAP_PROP_POS_FRAMES);
	/* Return to the beginning */
	cvSetCaptureProperty 
(input_video, CV_CAP_PROP_POS_FRAMES, 0.);
 
    IplImage * source[ 2 ], * image[ 2 ];
    source[ 0 ] = cvCreateImage (frame_size, IPL_DEPTH_8U, 1);
    source[ 1 ] = cvCreateImage (frame_size, IPL_DEPTH_8U, 1);
    image[ 0 ] = cvCreateImage(frame_size, IPL_DEPTH_8U, 3);
    image[ 1 ] = cvCreateImage(frame_size, IPL_DEPTH_8U, 3);
 
    int current_frame = 300;
    cvSetCaptureProperty
( input_video, CV_CAP_PROP_POS_FRAMES, current_frame);
 
    IplImage * frame = cvQueryFrame( input_video );
    if (frame == NULL) {
        /* Why did we get a NULL frame?  We shouldn't be at the end. */
        fprintf(stderr, 
"Error: Hmm. The end came sooner than we thought.\n");
        return -1;
    }
 
    cvConvertImage(frame, image[ 0 ], CV_CVTIMG_FLIP);
    ++current_frame;
    cvSetCaptureProperty
( input_video, CV_CAP_PROP_POS_FRAMES, current_frame);
 
    frame = cvQueryFrame( input_video );
	if (frame == NULL) {
        fprintf(stderr,
 "Error: Hmm. The end came sooner than we thought.\n");
		return -1;
    }
 
    cvConvertImage(frame, image[ 1 ], CV_CVTIMG_FLIP);
//    cvNamedWindow ("frm", CV_WINDOW_AUTOSIZE);
//    cvShowImage ("frm", image[ 0 ]);
 
    cvCvtColor (image[ 0 ], source[ 0 ], CV_BGR2GRAY);
    cvCvtColor (image[ 1 ], source[ 1 ], CV_BGR2GRAY);
 
    cvNamedWindow("Pic1", CV_WINDOW_AUTOSIZE);
    cvShowImage("Pic1", source[ 0 ]);
 
    cvNamedWindow("Pic2", CV_WINDOW_AUTOSIZE);
    cvShowImage("Pic2", source[ 1 ]);
 
    CvSize size;
    size = cvGetSize( source[ 0 ] );
 
    size.height /= 16;
    size.width  /= 16;
 
    IplImage * velocityX = cvCreateImage(size, IPL_DEPTH_32F, 1),
             * velocityY = cvCreateImage(size, IPL_DEPTH_32F, 1);
 
    cvCalcOpticalFlowBM (source[ 0 ], source[ 1 ],
                      cvSize(16, 16), cvSize(1, 1), cvSize(3, 2), 0, 
                      velocityX, velocityY);
 
 
    cvNamedWindow ("Horizontal", CV_WINDOW_AUTOSIZE);
    cvShowImage ("Horizontal", velocityX);
 
    cout << velocityX->height;
    cout << endl << velocityX->width;
 
    cvNamedWindow ("Vertical", CV_WINDOW_AUTOSIZE);
    cvShowImage ("Vertical", velocityY);
 
    cvWaitKey( 0 );
 
    cvDestroyWindow( "Pic1" );
    cvDestroyWindow( "Pic2" );
    cvDestroyWindow( "Horizontal" );
    cvDestroyWindow( "Vertical" );
 
    cvReleaseImage( &source[ 1 ] );
    cvReleaseImage( &source[ 0 ] );
    cvReleaseImage( &image[ 1 ] );
    cvReleaseImage( &image[ 0 ] );
    cvReleaseImage( &velocityY );
    cvReleaseImage( &velocityX );