Gst

Gst — Media library supporting arbitrary formats and filter graphs.

Synopsis


#include <gst/gst.h>


void                gst_init                            (int *argc,
                                                         char **argv[]);
gboolean            gst_init_check                      (int *argc,
                                                         char **argv[],
                                                         GError **err);
GOptionGroup*       gst_init_get_option_group           (void);
void                gst_deinit                          (void);
void                gst_version                         (guint *major,
                                                         guint *minor,
                                                         guint *micro,
                                                         guint *nano);
gchar*              gst_version_string                  (void);
gboolean            gst_segtrap_is_enabled              (void);
void                gst_segtrap_set_enabled             (gboolean enabled);
gboolean            gst_registry_fork_is_enabled        (void);
void                gst_registry_fork_set_enabled       (gboolean enabled);
gboolean            gst_update_registry                 (void);

Description

GStreamer is a framework for constructing graphs of various filters (termed elements here) that will handle streaming media. Any discreet (packetizable) media type is supported, with provisions for automatically determining source type. Formatting/framing information is provided with a powerful negotiation framework. Plugins are heavily used to provide for all elements, allowing one to construct plugins outside of the GST library, even released binary-only if license require (please don't).

GStreamer borrows heavily from both the OGI media pipeline and Microsoft's DirectShow, hopefully taking the best of both and leaving the cruft behind. Its interface is slowly getting stable.

The GStreamer library should be initialized with gst_init() before it can be used. You should pass pointers to the main argc and argv variables so that GStreamer can process its own command line options, as shown in the following example.

Example 1. Initializing the gstreamer library

int
main (int argc, char *argv[])
{
  // initialize the GStreamer library
  gst_init (&argc, &argv);
  ...
}


It's allowed to pass two NULL pointers to gst_init() in case you don't want to pass the command line args to GStreamer.

You can also use GOption to initialize your own parameters as shown in the next code fragment:

Example 2. Initializing own parameters when initializing gstreamer

static gboolean stats = FALSE;
...
int
main (int argc, char *argv[])
{
 GOptionEntry options[] = {
  {"tags", 't', 0, G_OPTION_ARG_NONE, &tags,
      N_("Output tags (also known as metadata)"), NULL},
  {NULL}
 };
 // must initialise the threading system before using any other GLib funtion
 if (!g_thread_supported ())
   g_thread_init (NULL);
 ctx = g_option_context_new ("[ADDITIONAL ARGUMENTS]");
 g_option_context_add_main_entries (ctx, options, GETTEXT_PACKAGE);
 g_option_context_add_group (ctx, gst_init_get_option_group ());
 if (!g_option_context_parse (ctx, &argc, &argv, &err)) {
   g_print ("Error initializing: %s\n", GST_STR_NULL (err->message));
   exit (1);
 }
 g_option_context_free (ctx);
...
}


Use gst_version() to query the library version at runtime or use the GST_VERSION_* macros to find the version at compile time. Optionally gst_version_string() returns a printable string.

The gst_deinit() call is used to clean up all internal resources used by GStreamer. It is mostly used in unit tests to check for leaks.

Last reviewed on 2006-08-11 (0.10.10)

Details

gst_init ()

void                gst_init                            (int *argc,
                                                         char **argv[]);

Initializes the GStreamer library, setting up internal path lists, registering built-in elements, and loading standard plugins.

This function should be called before calling any other GLib functions. If this is not an option, your program must initialise the GLib thread system using g_thread_init() before any other GLib functions are called.

Note

This function will terminate your program if it was unable to initialize GStreamer for some reason. If you want your program to fall back, use gst_init_check() instead.

WARNING: This function does not work in the same way as corresponding functions in other glib-style libraries, such as gtk_init(). In particular, unknown command line options cause this function to abort program execution.

argc : pointer to application's argc
argv : pointer to application's argv

gst_init_check ()

gboolean            gst_init_check                      (int *argc,
                                                         char **argv[],
                                                         GError **err);

Initializes the GStreamer library, setting up internal path lists, registering built-in elements, and loading standard plugins.

This function will return FALSE if GStreamer could not be initialized for some reason. If you want your program to fail fatally, use gst_init() instead.

This function should be called before calling any other GLib functions. If this is not an option, your program must initialise the GLib thread system using g_thread_init() before any other GLib functions are called.

argc : pointer to application's argc
argv : pointer to application's argv
err : pointer to a GError to which a message will be posted on error
Returns : TRUE if GStreamer could be initialized.

gst_init_get_option_group ()

GOptionGroup*       gst_init_get_option_group           (void);

Returns a GOptionGroup with GStreamer's argument specifications. The group is set up to use standard GOption callbacks, so when using this group in combination with GOption parsing methods, all argument parsing and initialization is automated.

This function is useful if you want to integrate GStreamer with other libraries that use GOption (see g_option_context_add_group() ).

If you use this function, you should make sure you initialise the GLib threading system as one of the very first things in your program (see the example at the beginning of this section).

Returns : a pointer to GStreamer's option group.

gst_deinit ()

void                gst_deinit                          (void);

Clean up any resources created by GStreamer in gst_init().

It is normally not needed to call this function in a normal application as the resources will automatically be freed when the program terminates. This function is therefore mostly used by testsuites and other memory profiling tools.

After this call GStreamer (including this method) should not be used anymore.


gst_version ()

void                gst_version                         (guint *major,
                                                         guint *minor,
                                                         guint *micro,
                                                         guint *nano);

Gets the version number of the GStreamer library.

major : pointer to a guint to store the major version number
minor : pointer to a guint to store the minor version number
micro : pointer to a guint to store the micro version number
nano : pointer to a guint to store the nano version number

gst_version_string ()

gchar*              gst_version_string                  (void);

This function returns a string that is useful for describing this version of GStreamer to the outside world: user agent strings, logging, ...

Returns : a newly allocated string describing this version of GStreamer.

gst_segtrap_is_enabled ()

gboolean            gst_segtrap_is_enabled              (void);

Some functions in the GStreamer core might install a custom SIGSEGV handler to better catch and report errors to the application. Currently this feature is enabled by default when loading plugins.

Applications might want to disable this behaviour with the gst_segtrap_set_enabled() function. This is typically done if the application wants to install its own handler without GStreamer interfering.

Returns : TRUE if GStreamer is allowed to install a custom SIGSEGV handler.

Since 0.10.10


gst_segtrap_set_enabled ()

void                gst_segtrap_set_enabled             (gboolean enabled);

Applications might want to disable/enable the SIGSEGV handling of the GStreamer core. See gst_segtrap_is_enabled() for more information.

enabled : whether a custom SIGSEGV handler should be installed.

Since 0.10.10


gst_registry_fork_is_enabled ()

gboolean            gst_registry_fork_is_enabled        (void);

By default GStreamer will perform a fork() when scanning and rebuilding the registry file.

Applications might want to disable this behaviour with the gst_registry_fork_set_enabled() function.

Returns : TRUE if GStreamer will use fork() when rebuilding the registry. On platforms without fork(), this function will always return FALSE.

Since 0.10.10


gst_registry_fork_set_enabled ()

void                gst_registry_fork_set_enabled       (gboolean enabled);

Applications might want to disable/enable the usage of fork() when rebuilding the registry. See gst_registry_fork_is_enabled() for more information.

On platforms without fork(), this function will have no effect on the return value of gst_registry_fork_is_enabled().

enabled : whether rebuilding the registry may fork

Since 0.10.10


gst_update_registry ()

gboolean            gst_update_registry                 (void);

Forces GStreamer to re-scan its plugin paths and update the default plugin registry.

Applications will almost never need to call this function, it is only useful if the application knows new plugins have been installed (or old ones removed) since the start of the application (or, to be precise, the first call to gst_init()) and the application wants to make use of any newly-installed plugins without restarting the application.

Applications should assume that the registry update is neither atomic nor thread-safe and should therefore not have any dynamic pipelines running (including the playbin and decodebin elements) and should also not create any elements or access the GStreamer registry while the update is in progress.

Note that this function may block for a significant amount of time.

Returns : TRUE if the registry has been updated successfully (does not imply that there were changes), otherwise FALSE.

Since 0.10.12

See Also

Check out both OGI's pipeline and Microsoft's DirectShow for some background.