gstreamercamerahandler class:

#include <QApplication>
#include <gst/rtsp/gstrtsptransport.h>
#include <gst/video/videooverlay.h>

#include <QDebug>

#include "gstreamercamerahandler.h"

static void on_pad_added (GstElement *element, GstPad *pad, void *data);

static void on_pad_added (GstElement *element, GstPad *pad, void *data)
{
    GstElement *camerasrcbin = GST_ELEMENT (data);
    GstElement *depay;
    GstPad *sinkpad;

    depay = gst_bin_get_by_name(GST_BIN(camerasrcbin), "mydepay");

    sinkpad = gst_element_get_static_pad (depay, "sink");
    gst_pad_link (pad, sinkpad);
    gst_object_unref (sinkpad);

    gst_element_set_state(camerasrcbin, GST_STATE_PAUSED);

    gst_object_ref(camerasrcbin); /* to keep in memory */

    qDebug() << "Pad added and srcbin put to pause.";
}

int gstreamerCameraHandler::createCameraSrcBin(QString location)
{
    GstBus     *bus;
    GstElement *source;
    GstElement *depay;
    GstElement *parser;
    GstElement *queue;

    GstPad *pad;

    cameraSrcBin = gst_bin_new(NULL);

    source = gst_element_factory_make("rtspsrc", "mysource");
    depay = gst_element_factory_make("rtph264depay", "mydepay");
    parser = gst_element_factory_make("h264parse", "myparser");
    queue = gst_element_factory_make("queue","myqueue");

    if(!cameraSrcBin || !source || !depay || !parser || !queue)
    {
        qDebug() << "Not all elements could be created.";
        return -1;
    }

    g_object_set(G_OBJECT(source), "location", (gchar*)location.toStdString().c_str() , NULL);
    g_object_set(G_OBJECT(source), "do-rtsp-keep-alive", (gboolean) true, NULL);
//    g_object_set(G_OBJECT(source), "async-handling", (gboolean) true, NULL);
//    g_object_set(G_OBJECT(source), "timeout", (guint64) 1000000, NULL);
//    g_object_set(G_OBJECT(source), "tcp-timeout", (guint64) 5000000, NULL);
    g_object_set(G_OBJECT(source), "retry", (guint32) 100, NULL);
    g_object_set(G_OBJECT(source), "udp-reconnect", (gboolean) true, NULL);
    g_object_set(G_OBJECT(source), "protocols", GST_RTSP_LOWER_TRANS_UDP, NULL);
    g_object_set(G_OBJECT(source), "user-id", (gchar*)"root", NULL);
    g_object_set(G_OBJECT(source), "user-pw", (gchar*)"pass", NULL);
    g_object_set(G_OBJECT(source), "latency", (guint32) 0, NULL);

    gst_bin_add_many(GST_BIN(cameraSrcBin), source, depay, parser, queue, NULL);
    gst_element_link_many(depay, parser, queue, NULL);

    pad = gst_element_get_static_pad(queue, "src");
    gst_element_add_pad(cameraSrcBin, gst_ghost_pad_new("src", pad));
    gst_object_unref(GST_OBJECT(pad));
    g_signal_connect (source , "pad-added", G_CALLBACK (on_pad_added), GST_ELEMENT (cameraSrcBin));

    gst_element_set_state(cameraSrcBin, GST_STATE_PLAYING);
    return 0;
}

gstreamerCameraHandler::gstreamerCameraHandler(QObject *parent, QString location) :
    QObject(parent)
{
    createCameraSrcBin(location);
}



GStreamerwidget class:

#include <QApplication>
#include <gst/video/videooverlay.h>
#include <qpainter.h>
#include <qthread.h>
#include "gstreamerwidget.h"

static GstBusSyncReply _bus_callback (GstBus *bus, GstMessage *message, gpointer user_data);

static GstBusSyncReply _bus_callback (GstBus *bus, GstMessage *message, gpointer user_data)
{
    if (GST_MESSAGE_TYPE (message) != GST_MESSAGE_ELEMENT)
        return GST_BUS_PASS;

    if (!gst_message_has_name (message, "prepare-window-handle"))
        return GST_BUS_PASS;

    qDebug("Got message of type %s from %s", GST_MESSAGE_TYPE_NAME(message),
           GST_ELEMENT_NAME (GST_MESSAGE_SRC (message)));

    GStreamerWidget* widget = (GStreamerWidget*) user_data;
    if(widget->winid != 0)
    {
        gst_video_overlay_set_window_handle(GST_VIDEO_OVERLAY (message->src), widget->winid);
    }
    gst_message_unref (message);

    return GST_BUS_DROP;
}

GStreamerWidget::GStreamerWidget(QWidget *parent) :
    QWidget(parent)
{
    leftOffset = 0;
    rightOffset = 0;
    topOffset = 0;
    bottomOffset = 0;
    winid = 0;

    cameraObject = NULL;
    pipeline = NULL;
}

GStreamerWidget::~GStreamerWidget()
{
    detachCamera();
}

int GStreamerWidget::constructPipeline()
{
    GstBus *bus;

    GstElement *decoder;
    GstElement *queue;
    GstElement *crop;
    GstElement *scale;
    GstElement *postproc;
    GstElement *sink;

    pipeline = gst_pipeline_new(NULL);

    decoder = gst_element_factory_make("vaapidecode", NULL);
    queue = gst_element_factory_make("queue", NULL);
    crop = gst_element_factory_make("videocrop", NULL);
    scale = gst_element_factory_make("videoscale", NULL);
    postproc = gst_element_factory_make("vaapipostproc", NULL);
    sink = gst_element_factory_make("vaapisink", NULL);


    if(!pipeline || !inputbin || !decoder || !queue || !crop || !scale || !postproc || !sink)
    {
        g_log(NULL, G_LOG_LEVEL_ERROR,
              "Not all elements could be created.\n");
        return -1;
    }

    g_object_set(G_OBJECT(scale), "add-borders", true, NULL);

    g_object_set(G_OBJECT(sink), "force-aspect-ratio", false, NULL);
    g_object_set(G_OBJECT(sink), "async", false, NULL);
    g_object_set(G_OBJECT(sink), "sync", false, NULL);

    gst_bin_add_many(GST_BIN(pipeline), inputbin, decoder, queue, crop, scale, postproc, sink, NULL);
    gst_element_link_many(inputbin, decoder, queue, crop, scale, postproc, sink, NULL);

    bus = gst_pipeline_get_bus(GST_PIPELINE(pipeline));
    gst_bus_set_sync_handler (bus, _bus_callback, this, NULL);
    gst_object_unref(bus);

    return 0;
}

void GStreamerWidget::attachCamera(BlueprintCamera* camera)
{
    if(pipeline == NULL)
    {
        cameraObject = camera;
        inputbin = cameraObject->getCameraHandler()->getCameraSrcBin();
        winid = this->winId();

        constructPipeline();
    }
}

void GStreamerWidget::detachCamera()
{
    if(pipeline != NULL)
    {
        gst_bin_remove(GST_BIN(pipeline), inputbin);
        gst_element_set_state(inputbin, GST_STATE_PAUSED);

        /* Remove the videosink explicitly, so we are sure that it is gone in time */
        GstElement* videosink;
        videosink = gst_bin_get_by_interface(GST_BIN(pipeline), GST_TYPE_VIDEO_OVERLAY);
        gst_bin_remove(GST_BIN(pipeline), videosink);

        gst_element_set_state(pipeline, GST_STATE_NULL);
        gst_object_unref(pipeline);
        pipeline = NULL;
    }
}

void GStreamerWidget::play()
{
    if(pipeline != NULL)
    {
        gst_element_set_state(pipeline, GST_STATE_PLAYING);
    }
}

void GStreamerWidget::pause()
{
    if(pipeline != NULL)
    {
        gst_element_set_state(pipeline, GST_STATE_PAUSED);
    }
}

void GStreamerWidget::mousePressEvent(QMouseEvent *event)
{
    qDebug() << "mouse click..." << event;

    //    if (this->parent()) {

    //    QWidget::mousePressEvent(event);

    emit signalCameraPressed(cameraObject);

    //    } else {
    //        if(this->isMaximized()) {
    //            this->showNormal();
    //        } else {
    //            this->showMaximized();
    //        }
    //    }
}