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82 lines
3.1 KiB
XML
82 lines
3.1 KiB
XML
<chapter id="chapter-dparams">
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<title>Dynamic Controllable Parameters</title>
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<sect1 id="section-dparams-getting-started">
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<title>Getting Started</title>
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<para>
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The controller subsystem offers a lightweight way to adjust gobject
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properties over stream-time.
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It works by using time-stamped value pairs that are queued for
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element-properties.
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At run-time the elements continously pull values changes for the
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current stream-time.
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</para>
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<para>
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This subsystem is contained within the
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<filename>gstcontroller</filename> library.
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You need to include the header in your application's source file:
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</para>
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<programlisting>
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...
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#include <gst/gst.h>
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#include <gst/controller/gstcontroller.h>
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...
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</programlisting>
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<para>
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Your application should link to the shared library <filename>gstreamer-controller</filename>.
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</para>
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<para>
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The <filename>gstreamer-controller</filename> library needs to be initialized
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when your application is run. This can be done after the the GStreamer
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library has been initialized.
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</para>
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<programlisting>
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...
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gst_init (&argc, &argv);
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gst_controller_init (&argc, &argv);
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...
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</programlisting>
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</sect1>
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<sect1 id="section-dparams-parameters">
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<title>Setting up parameter control</title>
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<para>
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The first step is to select the parameters that should be controlled.
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This returns a controller object that is needed to further adjust the
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behaviour.
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</para>
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<programlisting>
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controller = gst_object_control_properties(object, "prop1", "prop2",...);
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</programlisting>
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<para>
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Next we can select an interpolation mode. This mode controls how inbetween
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values are determined.
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The controller subsystem can e.g. fill gaps by smoothing parameter changes.
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Each controllable GObject property can be
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interpolated differently.
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</para>
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<programlisting>
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gst_controller_set_interpolation_mode(controller,"prop1",mode);
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</programlisting>
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<para>
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Finally one needs to set control points. These are time-stamped GValues.
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The values become active when the timestamp is reached. They still stay
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in the list. If e.g. the pipeline runs a loop (using a segmented seek),
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the control-curve gets repeated as well.
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</para>
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<programlisting>
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gst_controller_set (controller, "prop1" ,0 * GST_SECOND, value1);
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gst_controller_set (controller, "prop1" ,1 * GST_SECOND, value2);
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</programlisting>
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<para>
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The controller subsystem has a builtin live-mode. Even though a parameter
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has timestamped control-values assigned one can change the GObject
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property through <function>g_object_set()</function>.
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This is highly useful when binding the GObject properties to GUI widgets.
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When the user adjusts the value with the widget, one can set the GObject
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property and this remains active until the next timestamped value overrides.
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This also works with smoothed parameters.
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</para>
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</sect1>
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</chapter>
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