OpenCV – 02

Working with Videos in OpenCV

#include <stdio.h>
#include <cv.h>
#include <highgui.h>

int main(void)

{
    /* Create an object that decodes the input video stream. */
    CvCapture *input_video = cvCaptureFromFile("VideoPlay_Demo.avi");
    if (input_video == NULL)
    {
        /* Either the video didn't exist OR codec doesn't support */
        fprintf(stderr, "Error: Can't open video.\n");
        return -1;
    }


    /* Read the video's frame size out of the AVI. */
    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;
    number_of_frames = (int) cvGetCaptureProperty(input_video, CV_CAP_PROP_FRAME_COUNT);


    /* Create a windows called "VideoPlay_Demo" for output.
     * window automatically change its size to match the output. */
    cvNamedWindow("VideoPlay_Demo", CV_WINDOW_AUTOSIZE);


    long current_frame = 0;
    while(true)
    {
        static IplImage *frame = NULL;
        
        /* Go to the frame we want */
        cvSetCaptureProperty( input_video, CV_CAP_PROP_POS_FRAMES, current_frame );


        /* Get the next frame of the video */
        frame = cvQueryFrame( input_video );
        if (frame == NULL)
        {
            fprintf(stderr, "Error: Hmm. The end came sooner than we thought.\n");
            return -1;
        }
        
        /* Now display the image */
        cvShowImage("VideoPlay_Demo", frame);
        
        /* And wait for. If the argument is 0 then it waits forever otherwise it waits that number of milliseconds */
        cvWaitKey(60);
        current_frame++;
        if (current_frame < 0)
            current_frame = 0;
        if (current_frame >= number_of_frames - 1)
            current_frame = number_of_frames - 2;
    }
}


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