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Original commit message from CVS: sync with the current CVS glib API
270 lines
8.4 KiB
Text
270 lines
8.4 KiB
Text
<chapter id="cha-hello2">
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<title>Your second application</title>
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<para>
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In a previous chapter we created a first version of the helloworld
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application. We then explained a better way of creating the elements
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using factories identified by MIME types and the autoplugger.
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</para>
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<sect1>
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<title>Autoplugging helloworld </title>
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<para>
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We will create a second version of the helloworld application using
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autoplugging. Its source code is a bit more complicated but
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it can handle many more data types.
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</para>
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<para>
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We start by creating the main() of our program:
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</para>
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<programlisting>
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#include <gst/gst.h>
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static void gst_play_have_type (GstElement *typefind, GstCaps *caps, GstElement *pipeline);
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static void gst_play_cache_empty (GstElement *element, GstElement *pipeline);
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int
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main (int argc, char *argv[])
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{
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GstElement *disksrc;
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GstElement *pipeline;
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GstElement *autobin;
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GstElement *typefind;
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GstElement *cache;
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gst_init (&argc, &argv);
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if (argc != 2) {
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g_print ("usage: %s <filename>\n", argv[0]);
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exit (-1);
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}
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/* create a new pipeline to hold the elements */
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pipeline = gst_pipeline_new ("pipeline");
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g_assert (pipeline != NULL);
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/* create a disk reader */
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disksrc = gst_elementfactory_make ("disksrc", "disk_source");
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g_assert (disksrc != NULL);
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g_object_set (G_OBJECT (disksrc), "location", argv[1], NULL);
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gst_bin_add (GST_BIN (pipeline), disksrc);
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autobin = gst_bin_new ("autobin");
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cache = gst_elementfactory_make ("autoplugcache", "cache");
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g_signal_connect (G_OBJECT (cache), "cache_empty",
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G_CALLBACK (gst_play_cache_empty), pipeline);
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typefind = gst_elementfactory_make ("typefind", "typefind");
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g_signal_connect (G_OBJECT (typefind), "have_type",
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G_CALLBACK (gst_play_have_type), pipeline);
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gst_bin_add (GST_BIN (autobin), cache);
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gst_bin_add (GST_BIN (autobin), typefind);
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gst_element_connect (cache, "src", typefind, "sink");
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gst_element_add_ghost_pad (autobin, gst_element_get_pad (cache, "sink"), "sink");
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gst_bin_add (GST_BIN( pipeline), autobin);
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gst_element_connect (disksrc, "src", autobin, "sink");
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/* start playing */
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gst_element_set_state( GST_ELEMENT (pipeline), GST_STATE_PLAYING);
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while (gst_bin_iterate (GST_BIN (pipeline)));
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/* stop the pipeline */
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gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_NULL);
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gst_object_unref (GST_OBJECT (pipeline));
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exit(0);
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}
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</programlisting>
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<para>
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We start by constructing a 'disksrc' element and an 'autobin' element that
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holds the autoplugcache and the typefind element.
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</para>
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<para>
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We attach the "cache_empty" signal to gst_play_cache_empty and the
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"have_type" to our gst_play_have_type function (defined below).
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</para>
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<programlisting>
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static void
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gst_play_have_type (GstElement *typefind, GstCaps *caps, GstElement *pipeline)
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{
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GstElement *osssink;
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GstElement *new_element;
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GstAutoplug *autoplug;
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GstElement *autobin;
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GstElement *disksrc;
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GstElement *cache;
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GST_DEBUG (0,"GstPipeline: play have type\n");
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gst_element_set_state (pipeline, GST_STATE_PAUSED);
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disksrc = gst_bin_get_by_name (GST_BIN (pipeline), "disk_source");
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autobin = gst_bin_get_by_name (GST_BIN (pipeline), "autobin");
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cache = gst_bin_get_by_name (GST_BIN (autobin), "cache");
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// disconnect the typefind from the pipeline and remove it
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gst_element_disconnect (cache, "src", typefind, "sink");
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gst_bin_remove (GST_BIN (autobin), typefind);
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/* and an audio sink */
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osssink = gst_elementfactory_make("osssink", "play_audio");
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g_assert(osssink != NULL);
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autoplug = gst_autoplugfactory_make ("staticrender");
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g_assert (autoplug != NULL);
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new_element = gst_autoplug_to_renderers (autoplug,
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caps,
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osssink,
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NULL);
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if (!new_element) {
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g_print ("could not autoplug, no suitable codecs found...\n");
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exit (-1);
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}
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gst_element_set_name (new_element, "new_element");
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gst_bin_add (GST_BIN (autobin), new_element);
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g_object_set (G_OBJECT (cache), "reset", TRUE, NULL);
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gst_element_connect (cache, "src", new_element, "sink");
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gst_element_set_state (pipeline, GST_STATE_PLAYING);
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}
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</programlisting>
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<para>
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The _have_type function first sets the pipeline to the PAUSED state so that
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it can safely modify the pipeline. It then finds the elements it is going to
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manipulate in the pipeline with:
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</para>
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<programlisting>
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disksrc = gst_bin_get_by_name (GST_BIN (pipeline), "disk_source");
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autobin = gst_bin_get_by_name (GST_BIN (pipeline), "autobin");
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cache = gst_bin_get_by_name (GST_BIN (autobin), "cache");
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</programlisting>
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<para>
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Now we have a handle to the elements we are going to manipulate in
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the next step.
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</para>
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<para>
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We don't need the typefind element anymore so we remove it from the pipeline:
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</para>
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<programlisting>
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// disconnect the typefind from the pipeline and remove it
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gst_element_disconnect (cache, "src", typefind, "sink");
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gst_bin_remove (GST_BIN (autobin), typefind);
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</programlisting>
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<para>
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Our next step is to construct an element that can play the type we just
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detected. We are going to use the autoplugger to create an element that
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connects the type to an osssink. We add the new element to our
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autobin.
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</para>
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<programlisting>
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/* and an audio sink */
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osssink = gst_elementfactory_make("osssink", "play_audio");
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g_assert(osssink != NULL);
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autoplug = gst_autoplugfactory_make ("staticrender");
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g_assert (autoplug != NULL);
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new_element = gst_autoplug_to_renderers (autoplug,
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caps,
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osssink,
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NULL);
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if (!new_element) {
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g_print ("could not autoplug, no suitable codecs found...\n");
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exit (-1);
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}
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gst_element_set_name (new_element, "new_element");
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gst_bin_add (GST_BIN (autobin), new_element);
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</programlisting>
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<para>
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Our next step is to reset the cache so that the buffers used by the
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typefind element are fed into the new element we just created. We reset
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the cache by setting the "reset" property of the cache element to TRUE.
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</para>
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<programlisting>
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g_object_set (G_OBJECT (cache), "reset", TRUE, NULL);
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gst_element_connect (cache, "src", new_element, "sink");
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</programlisting>
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<para>
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Finally we set the pipeline back to the playing state. At this point the
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cache will replay the buffers. We will be notified when the cache is empty
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with the gst_play_cache_empty callback function:
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</para>
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<programlisting>
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static void
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gst_play_cache_empty (GstElement *element, GstElement *pipeline)
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{
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GstElement *autobin;
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GstElement *disksrc;
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GstElement *cache;
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GstElement *new_element;
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fprintf (stderr, "have cache empty\n");
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gst_element_set_state (pipeline, GST_STATE_PAUSED);
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disksrc = gst_bin_get_by_name (GST_BIN (pipeline), "disk_source");
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autobin = gst_bin_get_by_name (GST_BIN (pipeline), "autobin");
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cache = gst_bin_get_by_name (GST_BIN (autobin), "cache");
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new_element = gst_bin_get_by_name (GST_BIN (autobin), "new_element");
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gst_element_disconnect (disksrc, "src", cache, "sink");
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gst_element_disconnect (cache, "src", new_element, "sink");
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gst_bin_remove (GST_BIN (autobin), cache);
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gst_element_connect (disksrc, "src", new_element, "sink");
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gst_element_set_state (pipeline, GST_STATE_PLAYING);
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fprintf (stderr, "done with cache_empty\n");
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}
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</programlisting>
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<para>
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The cache empty function simply removes the autoplugcache element from
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the pipeline and reconnects the disksrc to the autoplugged element.
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</para>
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<para>
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To compile the helloworld2 example, use:
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</para>
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<programlisting>
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gcc -Wall `gstreamer-config --cflags --libs` helloworld2.c \
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-o helloworld2
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</programlisting>
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<para>
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You can run the example with (substitute helloworld.mp3 with you favorite MP3 file):
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</para>
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<programlisting>
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./helloworld2 helloworld.mp3
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</programlisting>
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<para>
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You can also try to use an AVI or MPEG file as its input. Using autoplugging,
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<application>GStreamer</application> will automatically figure out how to
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handle the stream. Remember that only the audio part will be played because
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we have only added an osssink to the pipeline.
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</para>
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<programlisting>
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./helloworld2 mymovie.mpeg
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</programlisting>
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</sect1>
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</chapter>
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