Interfaces

In Using an element as a GObject, you have learned how to use GObject properties as a simple way to do interaction between applications and elements. This method suffices for the simple'n'straight settings, but fails for anything more complicated than a getter and setter. For the more complicated use cases, GStreamer uses interfaces based on the GObject GTypeInterface type.

Most of the interfaces handled here will not contain any example code. See the API references for details. Here, we will just describe the scope and purpose of each interface.

The URI interface

In all examples so far, we have only supported local files through the “filesrc” element. GStreamer, obviously, supports many more location sources. However, we don't want applications to need to know any particular element implementation details, such as element names for particular network source types and so on. Therefore, there is a URI interface, which can be used to get the source element that supports a particular URI type. There is no strict rule for URI naming, but in general we follow naming conventions that others use, too. For example, assuming you have the correct plugins installed, GStreamer supports “file:///<path>/<file>”, “http://<host>/<path>/<file>”, “mms://<host>/<path>/<file>”, and so on.

In order to get the source or sink element supporting a particular URI, use gst_element_make_from_uri (), with the URI type being either GST_URI_SRC for a source element, or GST_URI_SINK for a sink element.

You can convert filenames to and from URIs using GLib's g_filename_to_uri () and g_uri_to_filename ().

The Color Balance interface

The colorbalance interface is a way to control video-related properties on an element, such as brightness, contrast and so on. It's sole reason for existence is that, as far as its authors know, there's no way to dynamically register properties using GObject.

The colorbalance interface is implemented by several plugins, including xvimagesink and the Video4linux2 elements.

The Video Overlay interface

The Video Overlay interface was created to solve the problem of embedding video streams in an application window. The application provides an window handle to the element implementing this interface to draw on, and the element will then use this window handle to draw on rather than creating a new toplevel window. This is useful to embed video in video players.

This interface is implemented by, amongst others, the Video4linux2 elements and by ximagesink, xvimagesink and sdlvideosink.

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