gstreamer/docs/libs/tmpl/gstcontrol.sgml

<!-- ##### SECTION Title ##### -->
gstcontrol

<!-- ##### SECTION Short_Description ##### -->
dynamic parameter functionality.

<!-- ##### SECTION Long_Description ##### -->
<para>
This library provides a manager component (#GstDParamManager) that maintains a
list of dynamically controlable parameters for a #GstElement.
Just think of a volume slider in a mixer.
</para>

<para>
#GstElement instances wanting to provide dynamic parameters, need to provide
a #GParamSpec and an update method. The application that will later use the
control parameter, will create a #DParam instance and attach that to use
provided #GParamSpec and update method.
The control library provides several #DParam implementations that can be used
interchangably. The base on just updated the parameter, while others can smooth
the control changes.
</para>

<para>
To use this library in a application one needs to add some code to initialize it.
<example>
<title>Adding the control library to an application (step 1)</title>
<programlisting>
...
&hash;include &lt;gst/gst.h&gt;
&hash;include &lt;gst/control/control.h&gt;
...
gst_init(&amp;argc,&amp;argv);
gst_control_init(&amp;argc,&amp;argv);
...
</programlisting>
</example>
</para>
<para>
The next step is to get hold of the #GstDParamManager instance of a #GstElement
and set the working mode of the manager.
<example>
<title>Adding the control library to an application (step 2)</title>
<programlisting>
dparam_manager=gst_dpman_get_manager(element);
gst_dpman_set_mode(dparam_manager, "synchronous");
</programlisting>
</example>
</para>

<para>
Finally one need to attach a new #DParam to the paramter spec.
<example>
<title>Adding the control library to an application (step 3)</title>
<programlisting>
pspec=gst_dpman_get_param_spec(dparam_manager,"volume");
dparam=gst_dparam_new(G_PARAM_SPEC_VALUE_TYPE(pspec));
gst_dpman_attach_dparam(dparam_manager,g_param_spec_get_name(pspecs),dparam);
</programlisting>
</example>
For a full example look at the <file>gst-plugins/gst/sine/demo-dparams.c</file>
</para>
<para>
To add dparam support to a plugin look at <file>gst-plugins/gst/sine/gstsinesrc.c</file>
or <file>gst-plugins/gst/volume/gstvolume.c</file>.
The key concept is to call GST_DPMAN_PREPROCESS() before processing data and to
wrap the data processing (chain or loop function) by GST_DPMAN_PROCESS().
This allows the manager to interupt processing to apply new control values.
</para>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### FUNCTION gst_control_init ##### -->
<para>

</para>

@argc: 
@argv: