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<chapter id="chapter-helloworld">
<title>Your first application</title>
This chapter will summarize everything you've learned in the previous
chapters. It describes all aspects of a simple &GStreamer; application,
including initializing libraries, creating elements, packing elements
together in a pipeline and playing this pipeline. By doing all this,
you will be able to build a simple Ogg/Vorbis audio player.
<sect1 id="section-helloworld">
<title>Hello world</title>
We're going to create a simple first application, a simple Ogg/Vorbis
command-line audio player. For this, we will use only standard
&GStreamer; components. The player will read a file specified on
the command-line. Let's get started!
We've learned, in <xref linkend="chapter-init"/>, that the first thing
to do in your application is to initialize &GStreamer; by calling
<function>gst_init ()</function>. Also, make sure that the application
includes <filename>gst/gst.h</filename> so all function names and
objects are properly defined. Use <function>#include
&lt;gst/gst.h&gt;</function> to do that.
Next, you'll want to create the different elements using
<function>gst_element_factory_make ()</function>. For an Ogg/Vorbis
audio player, we'll need a source element that reads files from a
disk. &GStreamer; includes this element under the name
<quote>filesrc</quote>. Next, we'll need something to parse the
file and decode it into raw audio. &GStreamer; has two elements
for this: the first parses Ogg streams into elementary streams (video,
audio) and is called <quote>oggdemux</quote>. The second is a Vorbis
audio decoder, it's conveniently called <quote>vorbisdec</quote>.
Since <quote>oggdemux</quote> creates dynamic pads for each elementary
stream, you'll need to set a <quote>pad-added</quote> event handler
on the <quote>oggdemux</quote> element, like you've learned in
<xref linkend="section-pads-dynamic"/>, to link the Ogg demuxer and
the Vorbis decoder elements together. At last, we'll also need an
audio output element, we will use <quote>autoaudiosink</quote>, which
automatically detects your audio device.
The last thing left to do is to add all elements into a container
element, a <classname>GstPipeline</classname>, and wait until
we've played the whole song. We've previously
learned how to add elements to a container bin in <xref
linkend="chapter-bins"/>, and we've learned about element states
in <xref linkend="section-elements-states"/>. We will also attach
a message handler to the pipeline bus so we can retrieve errors
and detect the end-of-stream.
Let's now add all the code together to get our very first audio
<!-- example-begin helloworld.c -->
#include &lt;gst/gst.h&gt;
#include &lt;glib.h&gt;
static gboolean
bus_call (GstBus *bus,
GstMessage *msg,
gpointer data)
GMainLoop *loop = (GMainLoop *) data;
switch (GST_MESSAGE_TYPE (msg)) {
g_print ("End of stream\n");
g_main_loop_quit (loop);
gchar *debug;
GError *error;
gst_message_parse_error (msg, &amp;error, &amp;debug);
g_free (debug);
g_printerr ("Error: %s\n", error->message);
g_error_free (error);
g_main_loop_quit (loop);
return TRUE;
static void
on_pad_added (GstElement *element,
GstPad *pad,
gpointer data)
GstPad *sinkpad;
GstElement *decoder = (GstElement *) data;
/* We can now link this pad with the vorbis-decoder sink pad */
g_print ("Dynamic pad created, linking demuxer/decoder\n");
sinkpad = gst_element_get_static_pad (decoder, "sink");
gst_pad_link (pad, sinkpad);
gst_object_unref (sinkpad);
main (int argc,
char *argv[])
GMainLoop *loop;
GstElement *pipeline, *source, *demuxer, *decoder, *conv, *sink;
GstBus *bus;
guint bus_watch_id;
/* Initialisation */
gst_init (&amp;argc, &amp;argv);
loop = g_main_loop_new (NULL, FALSE);
/* Check input arguments */
if (argc != 2) {
g_printerr ("Usage: %s &lt;Ogg/Vorbis filename&gt;\n", argv[0]);
return -1;
/* Create gstreamer elements */
pipeline = gst_pipeline_new ("audio-player");
source = gst_element_factory_make ("filesrc", "file-source");
demuxer = gst_element_factory_make ("oggdemux", "ogg-demuxer");
decoder = gst_element_factory_make ("vorbisdec", "vorbis-decoder");
conv = gst_element_factory_make ("audioconvert", "converter");
sink = gst_element_factory_make ("autoaudiosink", "audio-output");
if (!pipeline || !source || !demuxer || !decoder || !conv || !sink) {
g_printerr ("One element could not be created. Exiting.\n");
return -1;
/* Set up the pipeline */
/* we set the input filename to the source element */
g_object_set (G_OBJECT (source), "location", argv[1], NULL);
/* we add a message handler */
bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
bus_watch_id = gst_bus_add_watch (bus, bus_call, loop);
gst_object_unref (bus);
/* we add all elements into the pipeline */
/* file-source | ogg-demuxer | vorbis-decoder | converter | alsa-output */
gst_bin_add_many (GST_BIN (pipeline),
source, demuxer, decoder, conv, sink, NULL);
/* we link the elements together */
/* file-source -&gt; ogg-demuxer ~&gt; vorbis-decoder -&gt; converter -&gt; alsa-output */
gst_element_link (source, demuxer);
gst_element_link_many (decoder, conv, sink, NULL);
g_signal_connect (demuxer, "pad-added", G_CALLBACK (on_pad_added), decoder);
/* note that the demuxer will be linked to the decoder dynamically.
The reason is that Ogg may contain various streams (for example
audio and video). The source pad(s) will be created at run time,
by the demuxer when it detects the amount and nature of streams.
Therefore we connect a callback function which will be executed
when the "pad-added" is emitted.*/
/* Set the pipeline to "playing" state*/
g_print ("Now playing: %s\n", argv[1]);
gst_element_set_state (pipeline, GST_STATE_PLAYING);
/* Iterate */
g_print ("Running...\n");
g_main_loop_run (loop);
/* Out of the main loop, clean up nicely */
g_print ("Returned, stopping playback\n");
gst_element_set_state (pipeline, GST_STATE_NULL);
g_print ("Deleting pipeline\n");
gst_object_unref (GST_OBJECT (pipeline));
g_source_remove (bus_watch_id);
g_main_loop_unref (loop);
return 0;
<!-- example-end helloworld.c -->
We now have created a complete pipeline. We can visualise the
pipeline as follows:
<figure float="1" id="section-hello-img">
<title>The "hello world" pipeline</title>
<imagedata scale="75" fileref="images/hello-world.&image;" format="&IMAGE;" />
<sect1 id="section-helloworld-compilerun">
<title>Compiling and Running helloworld.c</title>
To compile the helloworld example, use: <command>gcc -Wall
helloworld.c -o helloworld
$(pkg-config --cflags --libs gstreamer-&GST_API_VERSION;)</command>.
&GStreamer; makes use of <command>pkg-config</command> to get compiler
and linker flags needed to compile this application.
If you're running a non-standard installation (ie. you've installed
GStreamer from source yourself instead of using pre-built packages),
make sure the <classname>PKG_CONFIG_PATH</classname> environment variable
is set to the correct location (<filename>$libdir/pkgconfig</filename>).
In the unlikely case that you are using an uninstalled GStreamer
setup (ie. gst-uninstalled), you will need to use libtool to build the
hello world program, like this: <command>libtool --mode=link gcc -Wall
helloworld.c -o helloworld
$(pkg-config --cflags --libs gstreamer-&GST_API_VERSION;)</command>.
You can run this example application with <command>./helloworld
file.ogg</command>. Substitute <filename>file.ogg</filename>
with your favourite Ogg/Vorbis file.
<sect1 id="section-hello-world-conclusion">
This concludes our first example. As you see, setting up a pipeline
is very low-level but powerful. You will see later in this manual how
you can create a more powerful media player with even less effort
using higher-level interfaces. We will discuss all that in <xref
linkend="part-highlevel"/>. We will first, however, go more in-depth
into more advanced &GStreamer; internals.
It should be clear from the example that we can very easily replace
the <quote>filesrc</quote> element with some other element that
reads data from a network, or some other data source element that
is better integrated with your desktop environment. Also, you can
use other decoders and parsers/demuxers to support other media types. You
can use another audio sink if you're not running Linux, but Mac OS X,
Windows or FreeBSD, or you can instead use a filesink to write audio
files to disk instead of playing them back. By using an audio card
source, you can even do audio capture instead of playback. All this
shows the reusability of &GStreamer; elements, which is its greatest