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103 lines
4.3 KiB
XML
103 lines
4.3 KiB
XML
<!-- ############ chapter ############# -->
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<chapter id="chapter-building-testapp">
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<title>Building a Test Application</title>
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<para>
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Often, you will want to test your newly written plugin in an as small
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setting as possible. Ususally, <filename>gst-launch</filename> is a
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good first step at testing a plugin. However, you will often need more
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testing features than gst-launch can provide, such as seeking, events,
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interactivity and more. Writing your own small testing program is the
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easiest way to accomplish this. This section explains - in a few words
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- how to do that. For a complete application development guide, see the
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<ulink type="http" url="../manual/index.html">Application Development
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Manual</ulink>.
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</para>
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<para>
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At the start, you need to initialize the &GStreamer; core library by
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calling <function>gst_init ()</function>. You can alternatively call
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<function>gst_init_with_popt_tables ()</function>, which will return
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a pointer to popt tables. You can then use libpopt to handle the
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given argument table, and this will finish the &GStreamer; intialization.
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</para>
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<para>
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You can create elements using <function>gst_element_factory_make ()</function>,
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where the first argument is the element type that you want to create,
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and the second argument is a free-form name. The example at the end uses
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a simple filesource - decoder - soundcard output pipeline, but you can
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use specific debugging elements if that's necessary. For example, an
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<classname>identity</classname> element can be used in the middle of
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the pipeline to act as a data-to-application transmitter. This can be
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used to check the data for misbehaviours or correctness in your test
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application. Also, you can use a <classname>fakesink</classname>
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element at the end of the pipeline to dump your data to the stdout
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(in order to do this, set the <function>dump</function> property to
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TRUE). Lastly, you can use the <classname>efence</classname> element
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(indeed, an eletric fence memory debugger wrapper element) to check
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for memory errors.
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</para>
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<para>
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During linking, your test application can use fixation or filtered caps
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as a way to drive a specific type of data to or from your element. This
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is a very simple and effective way of checking multiple types of input
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and output in your element.
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</para>
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<para>
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Running the pipeline happens through the <function>gst_bin_iterate ()</function>
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function. Note that during running, you should connect to at least the
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<quote>error</quote> and <quote>eos</quote> signals on the pipeline
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and/or your plugin/element to check for correct handling of this. Also,
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you should add events into the pipeline and make sure your plugin handles
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these correctly (with respect to clocking, internal caching, etc.).
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</para>
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<para>
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Never forget to clean up memory in your plugin or your test application.
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When going to the NULL state, your element should clean up allocated
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memory and caches. Also, it should close down any references held to
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possible support libraries. Your application should <function>unref ()</function>
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the pipeline and make sure it doesn't crash.
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</para>
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<programlisting>
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#include <gst/gst.h>
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gint
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main (gint arcg,
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gchar *argv[])
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{
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GstElement *pipeline, *filesrc, *decoder, *filter, *sink;
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/* initialization */
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gst_init (&argc, &argv);
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/* create elements */
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pipeline = gst_pipeline_new ("my_pipeline");
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filesrc = gst_element_factory_make ("filesrc", "my_filesource");
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decoder = gst_element_factory_make ("mad", "my_decoder");
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filter = gst_element_factory_make ("my_filter", "my_filter");
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sink = gst_element_factory_make ("osssink", "audiosink");
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g_object_set (G_OBJECT (filesrc), "location", argv[1], NULL);
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/* link everything together */
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gst_element_link_many (filesrc, decoder, filter, sink, NULL);
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gst_bin_add_many (GST_BIN (pipeline), filesrc, decoder, filter, sink, NULL);
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/* run */
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gst_element_set_state (pipeline, GST_STATE_PLAYING);
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while (gst_bin_iterate (GST_BIN (pipeline)));
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/* clean up */
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gst_element_set_state (pipeline, GST_STATE_NULL);
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gst_object_unref (GST_OBJECT (pipeline));
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return 0;
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}
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</programlisting>
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</chapter>
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