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87 lines
2.6 KiB
Text
87 lines
2.6 KiB
Text
<!-- ##### SECTION Title ##### -->
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gstcontrol
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<!-- ##### SECTION Short_Description ##### -->
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dynamic parameter functionality.
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<!-- ##### SECTION Long_Description ##### -->
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<para>
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This library provides a manager component (#GstDParamManager) that maintains a
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list of dynamically controlable parameters for a #GstElement.
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Just think of a volume slider in a mixer.
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</para>
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<para>
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#GstElement instances wanting to provide dynamic parameters, need to provide
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a #GParamSpec and an update method. The application that will later use the
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control parameter, will create a #DParam instance and attach that to use
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provided #GParamSpec and update method.
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The control library provides several #DParam implementations that can be used
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interchangably. The base on just updated the parameter, while others can smooth
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the control changes.
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</para>
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<para>
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To use this library in a application one needs to add some code to initialize it.
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<example>
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<title>Adding the control library to an application (step 1)</title>
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<programlisting>
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...
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&hash;include <gst/gst.h>
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&hash;include <gst/control/control.h>
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...
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gst_init(&argc,&argv);
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gst_control_init(&argc,&argv);
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...
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</programlisting>
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</example>
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</para>
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<para>
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The next step is to get hold of the #GstDParamManager instance of a #GstElement
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and set the working mode of the manager.
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<example>
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<title>Adding the control library to an application (step 2)</title>
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<programlisting>
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dparam_manager=gst_dpman_get_manager(element);
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gst_dpman_set_mode(dparam_manager, "synchronous");
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</programlisting>
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</example>
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</para>
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<para>
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Finally one need to attach a new #DParam to the paramter spec.
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<example>
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<title>Adding the control library to an application (step 3)</title>
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<programlisting>
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pspec=gst_dpman_get_param_spec(dparam_manager,"volume");
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dparam=gst_dparam_new(G_PARAM_SPEC_VALUE_TYPE(pspec));
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gst_dpman_attach_dparam(dparam_manager,g_param_spec_get_name(pspecs),dparam);
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</programlisting>
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</example>
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For a full example look at the <file>gst-plugins/gst/sine/demo-dparams.c</file>
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</para>
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<para>
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To add dparam support to a plugin look at <file>gst-plugins/gst/audiotestsrc/gstaudiotestsrc.c</file>
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or <file>gst-plugins/gst/volume/gstvolume.c</file>.
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The key concept is to call GST_DPMAN_PREPROCESS() before processing data and to
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wrap the data processing (chain or loop function) by GST_DPMAN_PROCESS().
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This allows the manager to interupt processing to apply new control values.
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</para>
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<!-- ##### SECTION See_Also ##### -->
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<para>
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</para>
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<!-- ##### SECTION Stability_Level ##### -->
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<!-- ##### FUNCTION gst_control_init ##### -->
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<para>
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</para>
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@argc:
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@argv:
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