GstVideo.VideoOverlay

g GObject.GInterface GObject.GInterface GstVideo.VideoOverlay GstVideo.VideoOverlay GObject.GInterface->GstVideo.VideoOverlay

Implementations:

None

Methods

class

install_properties (oclass, last_prop_id)

class

set_property (object, last_prop_id, property_id, value)

expose ()

got_window_handle (handle)

handle_events (handle_events)

prepare_window_handle ()

set_render_rectangle (x, y, width, height)

set_window_handle (handle)

Virtual Methods

do_expose ()

do_handle_events (handle_events)

do_set_render_rectangle (x, y, width, height)

do_set_window_handle (handle)

Properties

None

Signals

None

Fields

None

Class Details

class GstVideo.VideoOverlay
Bases:

GObject.GInterface

Structure:

GstVideo.VideoOverlayInterface

The GstVideo.VideoOverlay interface is used for 2 main purposes :

  • To get a grab on the Window where the video sink element is going to render. This is achieved by either being informed about the Window identifier that the video sink element generated, or by forcing the video sink element to use a specific Window identifier for rendering.

  • To force a redrawing of the latest video frame the video sink element displayed on the Window. Indeed if the Gst.Pipeline is in Gst.State.PAUSED state, moving the Window around will damage its content. Application developers will want to handle the Expose events themselves and force the video sink element to refresh the Window’s content.

Using the Window created by the video sink is probably the simplest scenario, in some cases, though, it might not be flexible enough for application developers if they need to catch events such as mouse moves and button clicks.

Setting a specific Window identifier on the video sink element is the most flexible solution but it has some issues. Indeed the application needs to set its Window identifier at the right time to avoid internal Window creation from the video sink element. To solve this issue a Gst.Message is posted on the bus to inform the application that it should set the Window identifier immediately. Here is an example on how to do that correctly:

static GstBusSyncReply
create_window (GstBus * bus, GstMessage * message, GstPipeline * pipeline)
{
 // ignore anything but 'prepare-window-handle' element messages
 if (!gst_is_video_overlay_prepare_window_handle_message (message))
   return GST_BUS_PASS;

 win = XCreateSimpleWindow (disp, root, 0, 0, 320, 240, 0, 0, 0);

 XSetWindowBackgroundPixmap (disp, win, None);

 XMapRaised (disp, win);

 XSync (disp, FALSE);

 gst_video_overlay_set_window_handle (GST_VIDEO_OVERLAY (GST_MESSAGE_SRC (message)),
     win);

 gst_message_unref (message);

 return GST_BUS_DROP;
}
...
int
main (int argc, char **argv)
{
...
 bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
 gst_bus_set_sync_handler (bus, (GstBusSyncHandler) create_window, pipeline,
        NULL);
...
}
Two basic usage scenarios

There are two basic usage scenarios: in the simplest case, the application uses #playbin or #playsink or knows exactly what particular element is used for video output, which is usually the case when the application creates the videosink to use (e.g. #xvimagesink, #ximagesink, etc.) itself; in this case, the application can just create the videosink element, create and realize the window to render the video on and then call GstVideo.VideoOverlay.set_window_handle() directly with the XID or native window handle, before starting up the pipeline. As #playbin and #playsink implement the video overlay interface and proxy it transparently to the actual video sink even if it is created later, this case also applies when using these elements.

In the other and more common case, the application does not know in advance what GStreamer video sink element will be used for video output. This is usually the case when an element such as #autovideosink is used. In this case, the video sink element itself is created asynchronously from a GStreamer streaming thread some time after the pipeline has been started up. When that happens, however, the video sink will need to know right then whether to render onto an already existing application window or whether to create its own window. This is when it posts a prepare-window-handle message, and that is also why this message needs to be handled in a sync bus handler which will be called from the streaming thread directly (because the video sink will need an answer right then).

As response to the prepare-window-handle element message in the bus sync handler, the application may use GstVideo.VideoOverlay.set_window_handle() to tell the video sink to render onto an existing window surface. At this point the application should already have obtained the window handle / XID, so it just needs to set it. It is generally not advisable to call any GUI toolkit functions or window system functions from the streaming thread in which the prepare-window-handle message is handled, because most GUI toolkits and windowing systems are not thread-safe at all and a lot of care would be required to co-ordinate the toolkit and window system calls of the different threads (Gtk+ users please note: prior to Gtk+ 2.18 GDK_WINDOW_XID was just a simple structure access, so generally fine to do within the bus sync handler; this macro was changed to a function call in Gtk+ 2.18 and later, which is likely to cause problems when called from a sync handler; see below for a better approach without GDK_WINDOW_XID used in the callback).

GstVideo.VideoOverlay and Gtk+
#include <gst/video/videooverlay.h>
#include <gtk/gtk.h>
#ifdef GDK_WINDOWING_X11
#include <gdk/gdkx.h>  // for GDK_WINDOW_XID
#endif
#ifdef GDK_WINDOWING_WIN32
#include <gdk/gdkwin32.h>  // for GDK_WINDOW_HWND
#endif
...
static guintptr video_window_handle = 0;
...
static GstBusSyncReply
bus_sync_handler (GstBus * bus, GstMessage * message, gpointer user_data)
{
 // ignore anything but 'prepare-window-handle' element messages
 if (!gst_is_video_overlay_prepare_window_handle_message (message))
   return GST_BUS_PASS;

 if (video_window_handle != 0) {
   GstVideoOverlay *overlay;

   // GST_MESSAGE_SRC (message) will be the video sink element
   overlay = GST_VIDEO_OVERLAY (GST_MESSAGE_SRC (message));
   gst_video_overlay_set_window_handle (overlay, video_window_handle);
 } else {
   g_warning ("Should have obtained video_window_handle by now!");
 }

 gst_message_unref (message);
 return GST_BUS_DROP;
}
...
static void
video_widget_realize_cb (GtkWidget * widget, gpointer data)
{
#if GTK_CHECK_VERSION(2,18,0)
  // Tell Gtk+/Gdk to create a native window for this widget instead of
  // drawing onto the parent widget.
  // This is here just for pedagogical purposes, GDK_WINDOW_XID will call
  // it as well in newer Gtk versions
  if (!gdk_window_ensure_native (widget->window))
    g_error ("Couldn't create native window needed for GstVideoOverlay!");
#endif

#ifdef GDK_WINDOWING_X11
  {
    gulong xid = GDK_WINDOW_XID (gtk_widget_get_window (video_window));
    video_window_handle = xid;
  }
#endif
#ifdef GDK_WINDOWING_WIN32
  {
    HWND wnd = GDK_WINDOW_HWND (gtk_widget_get_window (video_window));
    video_window_handle = (guintptr) wnd;
  }
#endif
}
...
int
main (int argc, char **argv)
{
  GtkWidget *video_window;
  GtkWidget *app_window;
  ...
  app_window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  ...
  video_window = gtk_drawing_area_new ();
  g_signal_connect (video_window, "realize",
      G_CALLBACK (video_widget_realize_cb), NULL);
  gtk_widget_set_double_buffered (video_window, FALSE);
  ...
  // usually the video_window will not be directly embedded into the
  // application window like this, but there will be many other widgets
  // and the video window will be embedded in one of them instead
  gtk_container_add (GTK_CONTAINER (ap_window), video_window);
  ...
  // show the GUI
  gtk_widget_show_all (app_window);

  // realize window now so that the video window gets created and we can
  // obtain its XID/HWND before the pipeline is started up and the videosink
  // asks for the XID/HWND of the window to render onto
  gtk_widget_realize (video_window);

  // we should have the XID/HWND now
  g_assert (video_window_handle != 0);
  ...
  // set up sync handler for setting the xid once the pipeline is started
  bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
  gst_bus_set_sync_handler (bus, (GstBusSyncHandler) bus_sync_handler, NULL,
      NULL);
  gst_object_unref (bus);
  ...
  gst_element_set_state (pipeline, GST_STATE_PLAYING);
  ...
}
GstVideo.VideoOverlay and Qt
#include <glib.h>;
#include <gst/gst.h>;
#include <gst/video/videooverlay.h>;

#include <QApplication>;
#include <QTimer>;
#include <QWidget>;

int main(int argc, char *argv[])
{
  if (!g_thread_supported ())
    g_thread_init (NULL);

  gst_init (&argc, &argv);
  QApplication app(argc, argv);
  app.connect(&app, SIGNAL(lastWindowClosed()), &app, SLOT(quit ()));

  // prepare the pipeline

  GstElement *pipeline = gst_pipeline_new ("xvoverlay");
  GstElement *src = gst_element_factory_make ("videotestsrc", NULL);
  GstElement *sink = gst_element_factory_make ("xvimagesink", NULL);
  gst_bin_add_many (GST_BIN (pipeline), src, sink, NULL);
  gst_element_link (src, sink);

  // prepare the ui

  QWidget window;
  window.resize(320, 240);
  window.show();

  WId xwinid = window.winId();
  gst_video_overlay_set_window_handle (GST_VIDEO_OVERLAY (sink), xwinid);

  // run the pipeline

  GstStateChangeReturn sret = gst_element_set_state (pipeline,
      GST_STATE_PLAYING);
  if (sret == GST_STATE_CHANGE_FAILURE) {
    gst_element_set_state (pipeline, GST_STATE_NULL);
    gst_object_unref (pipeline);
    // Exit application
    QTimer::singleShot(0, QApplication::activeWindow(), SLOT(quit()));
  }

  int ret = app.exec();

  window.hide();
  gst_element_set_state (pipeline, GST_STATE_NULL);
  gst_object_unref (pipeline);

  return ret;
}
classmethod install_properties(oclass, last_prop_id)
Parameters:

  • oclass (GObject.ObjectClass) – The class on which the properties will be installed

  • last_prop_id (int) – The first free property ID to use

This helper shall be used by classes implementing the GstVideo.VideoOverlay interface that want the render rectangle to be controllable using properties. This helper will install “render-rectangle” property into the class.

New in version 1.14.

classmethod set_property(object, last_prop_id, property_id, value)
Parameters:
Returns:

True if the property_id matches the GstVideo.VideoOverlay property

Return type:

bool

This helper shall be used by classes implementing the GstVideo.VideoOverlay interface that want the render rectangle to be controllable using properties. This helper will parse and set the render rectangle calling GstVideo.VideoOverlay.set_render_rectangle().

New in version 1.14.

expose()

Tell an overlay that it has been exposed. This will redraw the current frame in the drawable even if the pipeline is PAUSED.

got_window_handle(handle)
Parameters:

handle (int) – a platform-specific handle referencing the window

This will post a “have-window-handle” element message on the bus.

This function should only be used by video overlay plugin developers.

handle_events(handle_events)
Parameters:

handle_events (bool) – a bool indicating if events should be handled or not.

Tell an overlay that it should handle events from the window system. These events are forwarded upstream as navigation events. In some window system, events are not propagated in the window hierarchy if a client is listening for them. This method allows you to disable events handling completely from the GstVideo.VideoOverlay.

prepare_window_handle()

This will post a “prepare-window-handle” element message on the bus to give applications an opportunity to call GstVideo.VideoOverlay.set_window_handle() before a plugin creates its own window.

This function should only be used by video overlay plugin developers.

set_render_rectangle(x, y, width, height)
Parameters:

  • x (int) – the horizontal offset of the render area inside the window

  • y (int) – the vertical offset of the render area inside the window

  • width (int) – the width of the render area inside the window

  • height (int) – the height of the render area inside the window

Returns:

False if not supported by the sink.

Return type:

bool

Configure a subregion as a video target within the window set by GstVideo.VideoOverlay.set_window_handle(). If this is not used or not supported the video will fill the area of the window set as the overlay to 100%. By specifying the rectangle, the video can be overlayed to a specific region of that window only. After setting the new rectangle one should call GstVideo.VideoOverlay.expose() to force a redraw. To unset the region pass -1 for the width and height parameters.

This method is needed for non fullscreen video overlay in UI toolkits that do not support subwindows.

set_window_handle(handle)
Parameters:

handle (int) – a handle referencing the window.

This will call the video overlay’s set_window_handle method. You should use this method to tell to an overlay to display video output to a specific window (e.g. an XWindow on X11). Passing 0 as the handle will tell the overlay to stop using that window and create an internal one.

do_expose() virtual

Tell an overlay that it has been exposed. This will redraw the current frame in the drawable even if the pipeline is PAUSED.

do_handle_events(handle_events) virtual
Parameters:

handle_events (bool) – a bool indicating if events should be handled or not.

Tell an overlay that it should handle events from the window system. These events are forwarded upstream as navigation events. In some window system, events are not propagated in the window hierarchy if a client is listening for them. This method allows you to disable events handling completely from the GstVideo.VideoOverlay.

do_set_render_rectangle(x, y, width, height) virtual
Parameters:
do_set_window_handle(handle) virtual
Parameters:

handle (int) – a handle referencing the window.

This will call the video overlay’s set_window_handle method. You should use this method to tell to an overlay to display video output to a specific window (e.g. an XWindow on X11). Passing 0 as the handle will tell the overlay to stop using that window and create an internal one.