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<chapter id="chapter-init">
<title>Initializing &GStreamer;</title>
<para>
When writing a &GStreamer; application, you can simply include
<filename>gst/gst.h</filename> to get access to the library
functions. Besides that, you will also need to initialize the
&GStreamer; library.
</para>
<sect1 id="section-init-c">
<title>Simple initialization</title>
<para>
Before the &GStreamer; libraries can be used,
<function>gst_init</function> has to be called from the main
application. This call will perform the necessary initialization
of the library as well as parse the &GStreamer;-specific command
line options.
</para>
<para>
A typical program &EXAFOOT; would have code to initialize
&GStreamer; that looks like this:
</para>
<example id="ex-init-c">
<title>Initializing GStreamer</title>
<programlisting>
<!-- example-begin init.c -->
#include <stdio.h>
#include <gst/gst.h>
int
main (int argc,
char *argv[])
{
const gchar *nano_str;
guint major, minor, micro, nano;
gst_init (&argc, &argv);
gst_version (&major, &minor, &micro, &nano);
if (nano == 1)
nano_str = "(CVS)";
else if (nano == 2)
nano_str = "(Prerelease)";
else
nano_str = "";
printf ("This program is linked against GStreamer %d.%d.%d %s\n",
major, minor, micro, nano_str);
return 0;
}
<!-- example-end init.c -->
</programlisting>
</example>
<para>
Use the <symbol>GST_VERSION_MAJOR</symbol>,
<symbol>GST_VERSION_MINOR</symbol> and <symbol>GST_VERSION_MICRO</symbol>
macros to get the &GStreamer; version you are building against, or
use the function <function>gst_version</function> to get the version
your application is linked against. &GStreamer; currently uses a
scheme where versions with the same major and minor versions are
API-/ and ABI-compatible.
</para>
<para>
It is also possible to call the <function>gst_init</function> function
with two <symbol>NULL</symbol> arguments, in which case no command line
options will be parsed by <application>GStreamer</application>.
</para>
</sect1>
<sect1>
<title>The GOption interface</title>
<para>
You can also use a GOption table to initialize your own parameters as
shown in the next example:
</para>
<example id="ex-goption-c">
<title>Initialisation using the GOption interface</title>
<programlisting>
<!-- example-begin goption.c -->
#include <gst/gst.h>
int
main (int argc,
char *argv[])
{
gboolean silent = FALSE;
gchar *savefile = NULL;
GOptionContext *ctx;
GError *err = NULL;
GOptionEntry entries[] = {
{ "silent", 's', 0, G_OPTION_ARG_NONE, &silent,
"do not output status information", NULL },
{ "output", 'o', 0, G_OPTION_ARG_STRING, &savefile,
"save xml representation of pipeline to FILE and exit", "FILE" },
{ NULL }
};
ctx = g_option_context_new ("- Your application");
g_option_context_add_main_entries (ctx, entries, NULL);
g_option_context_add_group (ctx, gst_init_get_option_group ());
if (!g_option_context_parse (ctx, &argc, &argv, &err)) {
g_print ("Failed to initialize: %s\n", err->message);
g_error_free (err);
return 1;
}
printf ("Run me with --help to see the Application options appended.\n");
return 0;
}
<!-- example-end goption.c -->
</programlisting>
</example>
<para>
As shown in this fragment, you can use a <ulink
url="http://developer.gnome.org/glib/stable/glib-Commandline-option-parser.html"
type="http">GOption</ulink> table to define your application-specific
command line options, and pass this table to the GLib initialization
function along with the option group returned from the
function <function>gst_init_get_option_group</function>. Your
application options will be parsed in addition to the standard
<application>GStreamer</application> options.
</para>
</sect1>
</chapter>
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