Autoplugging

<chapter id="cha-autoplug">
  <title>Autoplugging</title>
  <para> 
    <application>GStreamer</application> provides an API to automatically
    construct complex pipelinebased on source and destination capabilities.
    This feature is very usefull if you want to convert type X to type Y but
    don't care about the plugins needed to accomplish this task. The 
    autoplugger will consult the plugin repository, select and connect the
    elements needed for the conversion.
  </para>
  <para> 
    The autoplugger API is implemented in an abstract class. Autoplugger implementations
    reside in plugins and are therefore optional and can be optimized for a specific
    task.  Two types of autopluggers exist: renderer ones and non
    renderer ones. the renderer autopluggers will not have any src pads while the
    non renderer ones do. The renderer autopluggers are mainly used for media
    playback while the non renderer ones are used for arbitrary format conversion.
  </para>

  <sect1>
    <title>Using autoplugging</title>
    <para> 
      You first need to create a suitable autoplugger with gst_autoplugfactory_make().
      The name of the autoplugger must be one of the registered autopluggers..
    </para>
    <para>
      A list of all available autopluggers can be obtained with gst_autoplugfactory_get_list().
    </para>
    <para>
      If the autoplugger supports the RENDERER API, use gst_autoplug_to_renderers() call to
      create a bin that connectes the src caps to the specified render elements. You can
      then add the bin to a pipeline and run it.

      <programlisting>

        GstAutoplug *autoplug;
	GstElement  *element;
	GstElement  *sink;

	/* create a static autoplugger */
	autoplug = gst_autoplugfactory_make ("staticrender");

	/* create an osssink */
	sink = gst_elementfactory_make ("osssink", "our_sink");

	/* create an element that can play audio/mp3 through osssink */
	element = gst_autoplug_to_renderers (autoplug,
	                                     gst_caps_new (
	                                       "sink_audio_caps",
	                                       "audio/mp3",
	                                       NULL
	                                     ),
	                                     sink,
	                                     NULL);

	/* add the element to a bin and connect the sink pad */
	...
      </programlisting>
    </para>
    <para>
      If the autoplugger supports the CAPS API, use the gst_autoplug_to_caps() function to
      connect the src caps to the destination caps. The created bin will have src and sink
      pads compatible with the provided caps.

      <programlisting>

        GstAutoplug *autoplug;
	GstElement  *element;

	/* create a static autoplugger */
	autoplug = gst_autoplugfactory_make ("static");

	/* create an element that converts audio/mp3 to audio/raw */
	element = gst_autoplug_to_caps (autoplug,
	                                gst_caps_new (
	                                  "sink_audio_caps",
	                                  "audio/mp3",
	                                  NULL
	                                ),
	                                gst_caps_new (
	                                  "src_audio_caps",
	                                  "audio/raw",
	                                  NULL
	                                ),
	                                NULL);

	/* add the element to a bin and connect the src/sink pads */
	...
      </programlisting>
    </para>
  </sect1>
  <sect1>
    <title>A complete autoplugging example</title>
    <para>
      We will create and explain how a complete media player can be built with the
      autoplugger.
    </para>
  </sect1>
</chapter>