<chapter id="cha-hello2">
<title>Your second application</title>
<para>
- In the previous chapter we created a first version of the helloworld
+ In a previous chapter we created a first version of the helloworld
application. We then explained a better way of creating the elements
- using factories identified by MIME types.
- </para>
- <para>
- In this chapter we will introduce you to autoplugging. Using the MIME
- types of the elements <application>GStreamer</application> can automatically create a pipeline
- for you.
+ using factories identified by MIME types and the autoplugger.
</para>
<sect1>
- <title>Autoplugging helloworld (outdated) </title>
+ <title>Autoplugging helloworld </title>
<para>
We will create a second version of the helloworld application using
- autoplugging. Its source code is considerably easier to write and
- it can also handle many more data types.
+ autoplugging. Its source code is a bit more complicated but
+ it can handle many more data types.
+ </para>
+ <para>
+ We start by creating the main() of our program:
</para>
<programlisting>
-
#include <gst/gst.h>
-static gboolean playing;
-
-/* eos will be called when the src element has an end of stream */
-void
-eos (GstSrc *src)
-{
- g_print ("have eos, quitting\n");
-
- playing = FALSE;
-}
+static void gst_play_have_type (GstElement *typefind, GstCaps *caps, GstElement *pipeline);
+static void gst_play_cache_empty (GstElement *element, GstElement *pipeline);
int
main (int argc, char *argv[])
{
- GstElement *disksrc, *audiosink;
+ GstElement *disksrc;
GstElement *pipeline;
+ GstElement *autobin;
+ GstElement *typefind;
+ GstElement *cache;
+
+ gst_init (&argc, &argv);
if (argc != 2) {
- g_print ("usage: %s <filename>\n", argv[0]);
+ g_print ("usage: %s <filename>\n", argv[0]);
exit (-1);
}
- gst_init (&argc, &argv);
-
- /* create a new bin to hold the elements */
+ /* create a new pipeline to hold the elements */
pipeline = gst_pipeline_new ("pipeline");
+ g_assert (pipeline != NULL);
/* create a disk reader */
disksrc = gst_elementfactory_make ("disksrc", "disk_source");
+ g_assert (disksrc != NULL);
g_object_set (G_OBJECT (disksrc), "location", argv[1], NULL);
- g_signal_connectc (G_OBJECT (disksrc), "eos",
- G_CALLBACK (eos), NULL, FALSE);
+ gst_bin_add (GST_BIN (pipeline), disksrc);
- /* and an audio sink */
- audiosink = gst_elementfactory_make ("audiosink", "play_audio");
+ autobin = gst_bin_new ("autobin");
+ cache = gst_elementfactory_make ("autoplugcache", "cache");
+ g_signal_connectc (G_OBJECT (cache), "cache_empty",
+ G_CALLBACK (gst_play_cache_empty), pipeline, FALSE);
- /* add objects to the main pipeline */
- gst_pipeline_add_src (GST_PIPELINE (pipeline), disksrc);
- gst_pipeline_add_sink (GST_PIPELINE (pipeline), audiosink);
+ typefind = gst_elementfactory_make ("typefind", "typefind");
+ g_signal_connectc (G_OBJECT (typefind), "have_type",
+ G_CALLBACK (gst_play_have_type), pipeline, FALSE);
+ gst_bin_add (GST_BIN (autobin), cache);
+ gst_bin_add (GST_BIN (autobin), typefind);
- if (!gst_pipeline_autoplug (GST_PIPELINE (pipeline))) {
- g_print ("unable to handle stream\n");
- exit (-1);
- }
+ gst_element_connect (cache, "src", typefind, "sink");
+ gst_element_add_ghost_pad (autobin, gst_element_get_pad (cache, "sink"), "sink");
- /* start playing */
- gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_PLAYING);
+ gst_bin_add (GST_BIN( pipeline), autobin);
+ gst_element_connect (disksrc, "src", autobin, "sink");
- playing = TRUE;
+ /* start playing */
+ gst_element_set_state( GST_ELEMENT (pipeline), GST_STATE_PLAYING);
- while (playing) {
- gst_bin_iterate (GST_BIN (pipeline));
- }
+ while (gst_bin_iterate (GST_BIN (pipeline)));
- /* stop the bin */
+ /* stop the pipeline */
gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_NULL);
- gst_pipeline_destroy (pipeline);
+ gst_object_unref (GST_OBJECT (pipeline));
- exit (0);
+ exit(0);
}
-
</programlisting>
-
<para>
- First of all, we do not use any mpg123 or mp3parse element in this example.
- In fact, we only specify a source element and a sink element and add them
- to a pipeline.
+ We start by constructing a 'disksrc' element and an 'autobin' element that
+ holds the autoplugcache and the typefind element.
</para>
-
<para>
- The most interesting change however is the following:
+ We attach the "cache_empty" signal to gst_play_cache_empty and the
+ "have_type" to our gst_play_have_type function (defined below).
</para>
+
<programlisting>
+static void
+gst_play_have_type (GstElement *typefind, GstCaps *caps, GstElement *pipeline)
+{
+ GstElement *osssink;
+ GstElement *new_element;
+ GstAutoplug *autoplug;
+ GstElement *autobin;
+ GstElement *disksrc;
+ GstElement *cache;
+
+ GST_DEBUG (0,"GstPipeline: play have type\n");
+
+ gst_element_set_state (pipeline, GST_STATE_PAUSED);
+
+ disksrc = gst_bin_get_by_name (GST_BIN (pipeline), "disk_source");
+ autobin = gst_bin_get_by_name (GST_BIN (pipeline), "autobin");
+ cache = gst_bin_get_by_name (GST_BIN (autobin), "cache");
- ...
- if (!gst_pipeline_autoplug (pipeline)) {
- g_print ("unable to handle stream\n");
+ // disconnect the typefind from the pipeline and remove it
+ gst_element_disconnect (cache, "src", typefind, "sink");
+ gst_bin_remove (GST_BIN (autobin), typefind);
+
+ /* and an audio sink */
+ osssink = gst_elementfactory_make("osssink", "play_audio");
+ g_assert(osssink != NULL);
+
+ autoplug = gst_autoplugfactory_make ("staticrender");
+ g_assert (autoplug != NULL);
+
+ new_element = gst_autoplug_to_renderers (autoplug,
+ caps,
+ osssink,
+ NULL);
+
+ if (!new_element) {
+ g_print ("could not autoplug, no suitable codecs found...\n");
exit (-1);
}
- ...
+ gst_element_set_name (new_element, "new_element");
+
+ gst_bin_add (GST_BIN (autobin), new_element);
+
+ g_object_set (G_OBJECT (cache), "reset", TRUE, NULL);
+
+ gst_element_connect (cache, "src", new_element, "sink");
+
+ gst_element_set_state (pipeline, GST_STATE_PLAYING);
+}
+ </programlisting>
+ <para>
+ The _have_type function first sets the pipeline to the PAUSED state so that
+ it can safely modify the pipeline. It then finds the elements it is going to
+ manipulate in the pipeline with:
+ </para>
+ <programlisting>
+ disksrc = gst_bin_get_by_name (GST_BIN (pipeline), "disk_source");
+ autobin = gst_bin_get_by_name (GST_BIN (pipeline), "autobin");
+ cache = gst_bin_get_by_name (GST_BIN (autobin), "cache");
</programlisting>
<para>
- This piece of code does all the magic.
+ Now we have a handle to the elements we are going to manipulate in
+ the next step.
</para>
+ <para>
+ We don't need the typefind element anymore so we remove it from the pipeline:
+ </para>
+ <programlisting>
+ // disconnect the typefind from the pipeline and remove it
+ gst_element_disconnect (cache, "src", typefind, "sink");
+ gst_bin_remove (GST_BIN (autobin), typefind);
+ </programlisting>
<para>
- <itemizedlist>
- <listitem>
- <para>
- The pipeline will try to connect the src and the sink element.
- </para>
- </listitem>
- <listitem>
- <para>
- Since the source has no type, a typedetection will be started on
- the source element.
- </para>
- </listitem>
- <listitem>
- <para>
- The best set of elements that connect the MIME type of the source
- element to the MIME type of the sink are found.
- </para>
- </listitem>
- <listitem>
- <para>
- The elements are added to the pipeline and their pads are connected.
- </para>
- </listitem>
- </itemizedlist>
+ Our next step is to construct an element that can play the type we just
+ detected. We are going to use the autoplugger to create an element that
+ connects the type to an osssink. We add the new element to our
+ autobin.
</para>
+ <programlisting>
+ /* and an audio sink */
+ osssink = gst_elementfactory_make("osssink", "play_audio");
+ g_assert(osssink != NULL);
+
+ autoplug = gst_autoplugfactory_make ("staticrender");
+ g_assert (autoplug != NULL);
+
+ new_element = gst_autoplug_to_renderers (autoplug,
+ caps,
+ osssink,
+ NULL);
+
+ if (!new_element) {
+ g_print ("could not autoplug, no suitable codecs found...\n");
+ exit (-1);
+ }
+
+ gst_element_set_name (new_element, "new_element");
+
+ gst_bin_add (GST_BIN (autobin), new_element);
+ </programlisting>
+
<para>
- After this autoplugging, the pipeline is ready to play. Remember that this
- pipeline will be able to playback all of the media types for which an
- appropriate plugin exists since the autoplugging is all done using MIME
- types.
+ Our next step is to reset the cache so that the buffers used by the
+ typefind element are fed into the new element we just created. We reset
+ the cache by setting the "reset" property of the cache element to TRUE.
</para>
+ <programlisting>
+ g_object_set (G_OBJECT (cache), "reset", TRUE, NULL);
+
+ gst_element_connect (cache, "src", new_element, "sink");
+ </programlisting>
+ <para>
+ Finally we set the pipeline back to the playing state. At this point the
+ cache will replay the buffers. We will be notified when the cache is empty
+ with the gst_play_cache_empty callback function:
+ <para>
+
+ <programlisting>
+static void
+gst_play_cache_empty (GstElement *element, GstElement *pipeline)
+{
+ GstElement *autobin;
+ GstElement *disksrc;
+ GstElement *cache;
+ GstElement *new_element;
+
+ fprintf (stderr, "have cache empty\n");
+
+ gst_element_set_state (pipeline, GST_STATE_PAUSED);
+
+ disksrc = gst_bin_get_by_name (GST_BIN (pipeline), "disk_source");
+ autobin = gst_bin_get_by_name (GST_BIN (pipeline), "autobin");
+ cache = gst_bin_get_by_name (GST_BIN (autobin), "cache");
+ new_element = gst_bin_get_by_name (GST_BIN (autobin), "new_element");
+
+ gst_element_disconnect (disksrc, "src", cache, "sink");
+ gst_element_disconnect (cache, "src", new_element, "sink");
+ gst_bin_remove (GST_BIN (autobin), cache);
+ gst_element_connect (disksrc, "src", new_element, "sink");
+
+ gst_element_set_state (pipeline, GST_STATE_PLAYING);
+
+ fprintf (stderr, "done with cache_empty\n");
+}
+ </programlisting>
<para>
- If you really want, you can use the GSteamer components to do the
- autoplugging yourself. We will cover this topic in the dynamic pipeline chapter.
+ The cache empty function simply removes the autoplugcache element from
+ the pipeline and reconnects the disksrc to the autoplugged element.
</para>
<para>
You can also try to use an AVI or MPEG file as its input. Using autoplugging,
<application>GStreamer</application> will automatically figure out how to
handle the stream. Remember that only the audio part will be played because
- we have only added an audiosink to the pipeline.
+ we have only added an osssink to the pipeline.
</para>
<programlisting>
./helloworld2 mymovie.mpeg
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