<refsect2> <para> The #GstVideoOverlay interface is used for 2 main purposes : <itemizedlist> <listitem> <para> 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. </para> </listitem> <listitem> <para> To force a redrawing of the latest video frame the video sink element displayed on the Window. Indeed if the #GstPipeline 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. </para> </listitem> </itemizedlist> </para> <para> 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. </para> <para> 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 #GstMessage 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;