gstreamer/docs/pwg/building-testapp.xml

<!-- ############ chapter ############# -->

<chapter id="chapter-building-testapp">
  <title>Building a Test Application</title>
  <para>
    Often, you will want to test your newly written plugin in an as small
    setting as possible. Usually, <filename>gst-launch</filename> is a
    good first step at testing a plugin. However, you will often need more
    testing features than gst-launch can provide, such as seeking, events,
    interactivity and more. Writing your own small testing program is the
    easiest way to accomplish this. This section explains - in a few words
    - how to do that. For a complete application development guide, see the
    <ulink type="http" url="../../manual/html/index.html">Application Development
    Manual</ulink>.
  </para>

    <para>
      At the start, you need to initialize the &GStreamer; core library by
      calling <function>gst_init ()</function>. You can alternatively call
      <function>gst_init_with_popt_tables ()</function>, which will return
      a pointer to popt tables. You can then use libpopt to handle the
      given argument table, and this will finish the &GStreamer; intialization.
    </para>

    <para>
      You can create elements using <function>gst_element_factory_make ()</function>,
      where the first argument is the element type that you want to create,
      and the second argument is a free-form name. The example at the end uses
      a simple filesource - decoder - soundcard output pipeline, but you can
      use specific debugging elements if that's necessary. For example, an
      <classname>identity</classname> element can be used in the middle of
      the pipeline to act as a data-to-application transmitter. This can be
      used to check the data for misbehaviours or correctness in your test
      application. Also, you can use a <classname>fakesink</classname>
      element at the end of the pipeline to dump your data to the stdout
      (in order to do this, set the <function>dump</function> property to
      TRUE). Lastly, you can use the <classname>efence</classname> element
      (indeed, an eletric fence memory debugger wrapper element) to check
      for memory errors.
    </para>

    <para>
      During linking, your test application can use fixation or filtered caps
      as a way to drive a specific type of data to or from your element. This
      is a very simple and effective way of checking multiple types of input
      and output in your element.
    </para>

    <para>
      Running the pipeline happens through the <function>gst_bin_iterate ()</function>
      function. Note that during running, you should connect to at least the
      <quote>error</quote> and <quote>eos</quote> signals on the pipeline
      and/or your plugin/element to check for correct handling of this. Also,
      you should add events into the pipeline and make sure your plugin handles
      these correctly (with respect to clocking, internal caching, etc.).
    </para>

    <para>
      Never forget to clean up memory in your plugin or your test application.
      When going to the NULL state, your element should clean up allocated
      memory and caches. Also, it should close down any references held to
      possible support libraries. Your application should <function>unref ()</function>
      the pipeline and make sure it doesn't crash.
    </para>

    <programlisting><!-- example-begin test.c -->
#include &lt;gst/gst.h&gt;

static gboolean
bus_call (GstBus     *bus,
	  GstMessage *msg,
	  gpointer    data)
{
  GMainLoop *loop = data;

  switch (GST_MESSAGE_TYPE (msg)) {
    case GST_MESSAGE_EOS:
      g_print ("End-of-stream\n");
      g_main_loop_quit (loop);
      break;
    case GST_MESSAGE_ERROR: {
      gchar *debug;
      GError *err;

      gst_message_parse_error (msg, &amp;err, &amp;debug);
      g_free (debug);

      g_print ("Error: %s\n", err->message);
      g_error_free (err);

      g_main_loop_quit (loop);
      break;
    }
    default:
      break;
  }

  return TRUE;
}

gint
main (gint   argc,
      gchar *argv[])
{
  GstElement *pipeline, *filesrc, *decoder, *filter, *sink;
  GMainLoop *loop;

  /* initialization */
  gst_init (&amp;argc, &amp;argv);
  loop = g_main_loop_new (NULL, FALSE);
  if (argc != 2) {
    g_print ("Usage: %s &lt;mp3 filename&gt;\n", argv[0]);
    return 01;
  }

  /* create elements */
  pipeline = gst_pipeline_new ("my_pipeline");
  gst_bus_add_watch (gst_pipeline_get_bus (GST_PIPELINE (pipeline)),
		     bus_call, loop);

  filesrc  = gst_element_factory_make ("filesrc", "my_filesource");
  decoder  = gst_element_factory_make ("mad", "my_decoder");
  filter   = gst_element_factory_make ("my_filter", "my_filter");
  sink     = gst_element_factory_make ("osssink", "audiosink");
  if (!sink || !decoder) {
    g_print ("Decoder or output could not be found - check your install\n");
    return -1;
  } else if (!filter) {
    g_print ("Your self-written filter could not be found. Make sure it "
             "is installed correctly in $(libdir)/gstreamer-0.9/ and that "
             "you've ran gst-register-0.9 to register it. Check availability "
             "of the plugin afterwards using \"gst-inspect-0.9 my_filter\"");
    return -1;
  }

  g_object_set (G_OBJECT (filesrc), "location", argv[1], NULL);

  /* link everything together */
  gst_element_link_many (filesrc, decoder, filter, sink, NULL);
  gst_bin_add_many (GST_BIN (pipeline), filesrc, decoder, filter, sink, NULL);

  /* run */
  gst_element_set_state (pipeline, GST_STATE_PLAYING);
  g_main_loop_run (loop);

  /* clean up */
  gst_element_set_state (pipeline, GST_STATE_NULL);
  gst_object_unref (GST_OBJECT (pipeline));

  return 0;
}
    <!-- example-end test.c --></programlisting>
</chapter>