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 function to access the next one.

I know of FFMPEG but it requiered to play with packets and things like that, and I'm surprised that nowhere on the net I can find a lib that allow something like :

Video v = openVideo("path");
uchar* data = v.getFrame();
v.nextFrame();

I just need to extract frames of a video to use it as a texture...no need for reencoding after or anything...

Of course something that would read the most format than possible would be great, something built upon libavcodec for example ;p

And I'm using Windows 7

Answer 1

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.