Interfaces

Using an element as a GObject presents the use of GObject properties as a simple way for applications and elements to interact. This method suffices for simple getters and setters, but fails for anything more complicated. For more complex use cases, GStreamer uses interfaces based on the GObject GTypeInterface type.

This text is meant to be introductory and does not include source code examples. Please take a look a the API reference for additional details.

The URI Handler interface

In our examples so far, we have only showed support for local files using the “filesrc” element, but GStreamer supports many more location sources.

GStreamer doesn't require applications to know any URI specifics, like what element to use for a particular network source types. These details are abstracted by the GstURIHandler interface.

There is no strict rule for URI naming, but in general, we follow common-usage naming conventions. For example, assuming you have the correct plugins installed, GStreamer supports:

file:///<path>/<file>
http://<host>/<path>/<file>
mms://<host>/<path>/<file>
dvb://<CHANNEL>
...

In order to get the source or sink element supporting a particular URI, use gst_element_make_from_uri () with GST_URI_SRC or GST_URI_SINK as GstURIType depending in the direction you need.

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 GstColorBalance 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, glimagesink and the Video4linux2 elements.

The Video Overlay interface

The GstVideoOverlay interface was created to solve the problem of embedding video streams in an application window. The application provides a window handle to an element implementing this interface, 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 glimagesink, ximagesink, xvimagesink and sdlvideosink.

Other interfaces

There are quite a few other interfaces provided by GStreamer and implemented by some of its elements. Among them:

  • GstChildProxy For access to internal element's properties on multi-child elements
  • GstNavigation For the sending and parsing of navigation events
  • GstPreset For handling element presets
  • GstRTSPExtension An RTSP Extension interface
  • GstStreamVolume Interface to provide access and control stream volume levels
  • GstTagSetter For handling media metadata
  • GstTagXmpWriter For elements that provide XMP serialization
  • GstTocSetter For setting and retrieval of TOC-like data
  • GstTuner For elements providing RF tunning operations
  • GstVideoDirection For video rotation and flipping controls
  • GstVideoOrientation For video orientation controls
  • GstWaylandVideo Wayland video interface

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