Gstreamer pull sample takes too long

Question

I have made the following code to retrieve the buffer data from a stream:

cv::Mat VideoFrameProcessing::getFrameFromGST()
{
    cv::Mat _temp_frame;

    int w, h;
    int num, den;
    GstStructure* structure;
    GstMapInfo map; 

    current_gst.sink = gst_bin_get_by_name(GST_BIN(current_gst.pipeline), "stream");
    if (!current_gst.sink)
        logNeuralAndPrint("ERROR: Sink es nulo");   

    current_gst.appsink = GST_APP_SINK(current_gst.sink);
    if (!current_gst.appsink)
    {
        logNeuralAndPrint("ERROR: Appsink es nulo");
        gst_object_unref(current_gst.sink);
    }

    current_gst.sample = gst_app_sink_pull_sample(current_gst.appsink);
    if (!current_gst.sample)
    {
        logNeuralAndPrint("ERROR: Sample es nulo");
        gst_object_unref(current_gst.sink);
    }


    current_gst.buffer = gst_sample_get_buffer(current_gst.sample);
    if (!current_gst.buffer)
    {
        logNeuralAndPrint("ERROR: El buffer es nulo");
        gst_sample_unref(current_gst.sample);
        gst_object_unref(current_gst.sink);
    }

    current_gst.caps = gst_sample_get_caps(current_gst.sample);
    structure = gst_caps_get_structure(current_gst.caps, 0);

    if(gst_structure_get_fraction(structure, "framerate", &num, &den))
        current_gst.framecount = static_cast<double>(num) / static_cast<double>(den);

    memset(&map, 0, sizeof(map));

    if (gst_buffer_map(current_gst.buffer, &map, GST_MAP_READ))
    {
        gst_structure_get_int(structure, "width", &w);
        gst_structure_get_int(structure, "height", &h);

        _temp_frame = cv::Mat(h, w, CV_8UC3, (void*)map.data, w * 3).clone();
        gst_buffer_unmap(current_gst.buffer, &map);
    }
    else
        logNeuralAndPrint("ERROR: No se puede mapear el buffer");

    gst_sample_unref(current_gst.sample);
    gst_object_unref(current_gst.sink);

    return _temp_frame;
}

My problem is that the function

current_gst.sample = gst_app_sink_pull_sample(current_gst.appsink);

takes too long to execute (but only the first time is called upon the start of the program) does anyone know why and how I can reduce the time it takes ?

For reference, some other parts of this same code take around 0.002 ms while this line takes 5000.00 ms.