mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-12-28 19:20:35 +00:00
ad1970eae2
Original commit message from CVS: 2005-07-15 Andy Wingo <wingo@pobox.com> * tools/gst-typefind.c: Update, add copyright block. * gst/base/gstbasesrc.c (gst_base_src_default_negotiate): Normalize and truncate caps before fixation. * gst/gstcaps.h: * gst/gstcaps.c (gst_caps_truncate): New function, destructively discards all but the first structure from its argument.
87 lines
2.6 KiB
Text
87 lines
2.6 KiB
Text
<!-- ##### 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 <gst/gst.h>
|
|
&hash;include <gst/control/control.h>
|
|
...
|
|
gst_init(&argc,&argv);
|
|
gst_control_init(&argc,&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>
|
|
|
|
<!-- ##### SECTION Stability_Level ##### -->
|
|
|
|
|
|
<!-- ##### FUNCTION gst_control_init ##### -->
|
|
<para>
|
|
|
|
</para>
|
|
|
|
@argc:
|
|
@argv:
|
|
|
|
|