OpenCV and GoPro - empty frames in VideoCapture st

问题:

I have a GoPro Hero 3+ (Black) which is connected to a video capture card (AverMedia Game Broadcaster HD). I simply want to get the video stream in OpenCV. With a Logitech Webcam there are no problems. The used code is below.

VideoCapture cap;
cap.open(0);

waitKey(300);

//cap.set(CV_CAP_PROP_FRAME_WIDTH, 1280);
//cap.set(CV_CAP_PROP_FRAME_HEIGHT, 720);

if (cap.isOpened()){
    cout << "Cam identified" << endl;
}

namedWindow("dst", 1);

while (1){

Mat frame;

if (!cap.read(frame)) {
    std::cout << "Unable to read frame from video stream" << std::endl;
    continue;
}

imshow("dst", frame);

[...]

}

With the GoPro the following happens: OpenCV is able to open the VideoCapture ("Cam identified") but can't read any frames (just a gray screen and the output: "Unable to read frame from video stream"). I also checked this with frame.empty();.

I know that the video capture card works correct because Unity opens a WebCamTexture with the GoPro stream without any issues. I read about codec problems in OpenCv and so I already tried to compile OpenCV with FFMPEG support. Now the recorded MP4-Videos of the GoPro can be displayed but the stream still doesn't work.

I use OpenCV 2.48, Windows 7 and Visual Studio 2013.

---

EDIT: Here is the code of libVLC solution:

struct ctx
{
uint8_t* pixeldata;
std::mutex imagemutex;
};

static void display(void *data, void *id);
static void unlock(void *data, void *id, void *const *p_pixels);
static void *lock(void *data, void **p_pixels);

struct ctx ctx;

libvlc_instance_t *inst;
libvlc_media_player_t *mp;
libvlc_media_t *m;

int main(int argc, char* argv[])
{
    ctx.pixeldata = new uint8_t[1280 * 720 * 3];

    char const *vlc_argv[] =
    {
        "-vvv",
        "--no-audio", /* skip any audio track */
        "--no-xlib", /* tell VLC to not use Xlib */
    };

    int vlc_argc = sizeof(vlc_argv) / sizeof(*vlc_argv);
    inst = libvlc_new(vlc_argc, vlc_argv);

    const char *options[] =
    {
        ":dshow-vdev=AVerMedia HD Capture",
        ":dshow-adev=none",
        //":dshow-size=1280x720",
        ":dshow-fps=24",
        ":dshow-chroma=YUY2",
        ":dshow-video-input=1",
        ":dshow-video-output=1",
        ":dshow-aspect-ratio=16\:9",
        ":live-caching=80",
        NULL
    };

    m = libvlc_media_new_location(inst, "dshow://");
    for (const char **opt = options; *opt; opt++)
        libvlc_media_add_option(m, *opt);

    mp = libvlc_media_player_new_from_media(m);
    libvlc_media_release(m);
    libvlc_video_set_callbacks(mp, lock, unlock, display, &ctx);
    libvlc_video_set_format(mp, "RV24", 1280, 720, 1280 * 3);
    libvlc_media_player_play(mp);

    namedWindow("all", 1);

    Mat frame(720, 1280, CV_8UC3);

    while (1){

        ctx.imagemutex.lock();
        memcpy(gesamt.data, ctx.pixeldata, 1280 * 720 * sizeof(uint8_t) * 3);
        ctx.imagemutex.unlock();

        imshow("all", gesamt);

        if (waitKey(30) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
        {
            cout << "esc key is pressed by user" << endl;
            break;
        }

    }

    libvlc_media_player_stop(mp);
    libvlc_media_player_release(mp);
    libvlc_release(inst);
    delete[] ctx.pixeldata;

    return 0;
}

void display(void *data, void *id){
    (void)data;
    assert(id == NULL);
}

void unlock(void *data, void *id, void *const *p_pixels){
    struct ctx *ctx = (struct ctx*)data;
    ctx->imagemutex.unlock();
    assert(id == NULL);
}

void *lock(void *data, void **p_pixels){
    struct ctx *ctx = (struct ctx*)data;
    ctx->imagemutex.lock();
    *p_pixels = ctx->pixeldata;
    return NULL;
}

回答1:

I've had the same issues trying to stream a Sony action cam through an Avermedia capture card. One quick fix seems to be using DVDrive, which makes your capture card output look like a webcam. I've had success using this as a workaround.