Simple frame by frame video decoder library

Question

I\'m looking for a simple c/c++ lib that would allow to extract the first frame of a video as a uchar array. And have a simple fonction to access the next one.

I kno

Answer 1

Use DirectShow. Here's an article: http://www.codeproject.com/KB/audio-video/framegrabber.aspx There are DirectShow 'add-ons' to decode different video formats. Here's one of the sites where you can grab free DirectShow filter packs to decode some common formats that are not directly supported by DirectShow: http://www.free-codecs.com/download/DirectShow_FilterPack.htm

Answer 2

You can use OpenCV it is very simple and they have a useful manual on their site http://opencv.willowgarage.com/wiki/

Answer 3

Here's an example with OpenCV:

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

int
main(int argc, char **argv)
{       
    cv::VideoCapture capture(argv[1]);
    if (capture.grab())
    {   
        cv::Mat_<char> frame;
        capture.retrieve(frame);
        //
        // Convert to your byte array here
        //
    }    
    return 0;
}

It's untested, but I cannibalized it from some existing working code, so it shouldn't take you long to get it working.

The cv::Mat_<unsigned char> is essentially a byte array. If you really need something that's explicitly of type unsigned char *, then you can malloc space of the appropriate size and iterate over the matrix using

You can convert a cv::Mat to a byte array using pixel positions(cv::Mat_::at()) or iterators (cv::Mat_::begin() and friends).

There are many reasons why libraries rarely expose image data as a simple pointer, such as:

• It implies the entire image must occupy a contiguous space in memory. This is a big deal when dealing with large images
• It requires committing a certain ordering of the data (pixel vs non-planar -- are the RGB planes stored interspersed or separately?) and reduces flexibility
• Dereferencing pointers is a cause for bugs (buffer overruns, etc).

So if you want your pointer, you have to do a bit of work for it.