Streaming a camera to memory using libvlc and displaying a frame

I am trying to transfer a grabber (camera) into memory using libvlc.

I am unable to display an image from the data stored in memory. The memory content looks fine. I tested it with Visual Studio and its memory windows. The image created by imshow is always gray. How can I display the image stored in memory?

My code is mostly based on this section

Thank.

using namespace cv; 
using namespace std;

HANDLE hMutex;

struct VideoDataStruct
{
    int param;
};

int done = 0;
libvlc_media_player_t *mp;
unsigned int videoBufferSize = 0;
uint8_t *videoBuffer = 0;

void cbVideoPrerender(void *p_video_data, uint8_t **pp_pixel_buffer, int size) {
    // Locking
    //HANDLE hMutex = ::OpenMutex(SYNCHRONIZE, FALSE, _T("my_mutex"));

    if (size > videoBufferSize || !videoBuffer)
    {
        printf("Reallocate raw video buffer\n");
        free(videoBuffer);
        videoBuffer = (uint8_t *) malloc(size);
        videoBufferSize = size;
    }

    // videoBuffer = (uint8_t *)malloc(size);
    *pp_pixel_buffer = videoBuffer;
}  
void cbVideoPostrender(void *p_video_data, uint8_t *p_pixel_buffer, int width, int height, int pixel_pitch, int size, int64_t pts) {
    // Unlocking
    //CloseHandle(hMutex);

}
static void handleEvent(const libvlc_event_t* pEvt, void* pUserData)
{
    libvlc_time_t time;
    switch(pEvt->type)
    {
        case libvlc_MediaPlayerTimeChanged:
            time = libvlc_media_player_get_time(mp);
            printf("MediaPlayerTimeChanged %lld ms\n", (long long)time);
            break;
        case libvlc_MediaPlayerEndReached:
            printf ("MediaPlayerEndReached\n");
            done = 1;
            break;
        default:
            printf("%s\n", libvlc_event_type_name(pEvt->type));
    }
}


int _tmain(int argc, _TCHAR* argv[])
 {
    hMutex = CreateMutex( NULL, FALSE, _T("my_mutex"));

    cout << "Test";

    // VLC pointers 
    libvlc_instance_t *inst;
    libvlc_media_t *m;
    void *pUserData = 0;

    VideoDataStruct dataStruct;

    // VLC options
    char smem_options[1000];

    // RV24
    sprintf(smem_options
        , "#transcode{vcodec=RV24}:smem{"
         "video-prerender-callback=%lld,"
         "video-postrender-callback=%lld,"
         "video-data=%lld,"
         "no-time-sync},"
        , (long long int)(intptr_t)(void*)&cbVideoPrerender
        , (long long int)(intptr_t)(void*)&cbVideoPostrender
        , (long long int)(intptr_t)(void*)&dataStruct
    );

    const char * const vlc_args[] = {
              "-I", "dummy",            // Don't use any interface
              "--ignore-config",        // Don't use VLC config
              "--extraintf=logger",     // Log anything
              "--verbose=1",            // Be verbose
              "--sout", smem_options    // Stream to memory
               };

    // We launch VLC
    inst = libvlc_new(sizeof(vlc_args) / sizeof(vlc_args[0]), vlc_args);

    /* Create a new item */
    m = libvlc_media_new_location(inst, "dshow://");

    /* Create a media player playing environement */
    mp = libvlc_media_player_new_from_media (m);

    libvlc_event_manager_t* eventManager = libvlc_media_player_event_manager(mp);
    libvlc_event_attach(eventManager, libvlc_MediaPlayerTimeChanged, handleEvent, pUserData);
    libvlc_event_attach(eventManager, libvlc_MediaPlayerEndReached, handleEvent, pUserData);
    libvlc_event_attach(eventManager, libvlc_MediaPlayerPositionChanged, handleEvent, pUserData);

    //libvlc_video_set_format(mp, "RV24", 240, 320, 240 * 3 );

    /* play the media_player */
    libvlc_media_player_play (mp);

    while(1)
    {
        if(videoBuffer)                                             // Check for invalid input
        {
            // CV_8UC3 = 8 bits, 3 chanels
            Mat img = Mat(Size(240, 320), CV_8UC3, videoBuffer);
            // cvtColor(img, img, CV_RGB2BGR);
            namedWindow("Display window", WINDOW_AUTOSIZE);         // Create a window for display.
            imshow("Display window", img);                          // Show our image inside it.
        }
    }
    Sleep (500000); /* Let it play a bit */
    libvlc_release (inst);
}