Overview

Using this API, applications can request the installation of missing GStreamer plugins. These may be missing decoders/demuxers or encoders/muxers for a certain format, sources or sinks for a certain URI protocol (e.g. 'http'), or certain elements known by their element factory name ('audioresample').

Whether plugin installation is supported or not depends on the operating system and/or distribution in question. The vendor of the operating system needs to make sure the necessary hooks and mechanisms are in place for plugin installation to work. See below for more detailed information.

From the application perspective, plugin installation is usually triggered either

Detail Strings

The install functions in this section all take one or more 'detail strings'. These detail strings contain information about the type of plugin that needs to be installed (decoder, encoder, source, sink, or named element), and some additional information such GStreamer version used and a human-readable description of the component to install for user dialogs.

Applications should not concern themselves with the composition of the string itself. They should regard the string as if it was a shared secret between GStreamer and the plugin installer application.

Detail strings can be obtained using the function gst_missing_plugin_message_get_installer_detail() on a missing-plugin message. Such a message will either have been found by the application on a pipeline's GstBus, or the application will have created it itself using gst_missing_element_message_new(), gst_missing_decoder_message_new(), gst_missing_encoder_message_new(), gst_missing_uri_sink_message_new(), or gst_missing_uri_source_message_new().

Plugin Installation from the Application Perspective

For each GStreamer element/plugin/component that should be installed, the application needs one of those 'installer detail' string mentioned in the previous section. This string can be obtained, as already mentioned above, from a missing-plugin message using the function gst_missing_plugin_message_get_installer_detail(). The missing-plugin message is either posted by another element and then found on the bus by the application, or the application has created it itself as described above.

The application will then call gst_install_plugins_async(), passing a NULL-terminated array of installer detail strings, and a function that should be called when the installation of the plugins has finished (successfully or not). Optionally, a GstInstallPluginsContext created with gst_install_plugins_context_new() may be passed as well. This way additional optional arguments like the application window's XID can be passed to the external installer application.

gst_install_plugins_async() will return almost immediately, with the return code indicating whether plugin installation was started or not. If the necessary hooks for plugin installation are in place and an external installer application has in fact been called, the passed in function will be called with a result code as soon as the external installer has finished. If the result code indicates that new plugins have been installed, the application will want to call gst_update_registry() so the run-time plugin registry is updated and the new plugins are made available to the application.

g_main_context_iteration (NULL,FALSE);

Plugin Installation from the Vendor/Distribution Perspective

1. Installer hook

When GStreamer applications initiate plugin installation via gst_install_plugins_async() or gst_install_plugins_sync(), a pre-defined helper application will be called.

The exact path of the helper application to be called is set at compile time, usually by the ./configure script based on the install prefix. For a normal package build into the /usr prefix, this will usually default to /usr/libexec/gst-install-plugins-helper or /usr/lib/gst-install-plugins-helper.

Vendors/distros who want to support GStreamer plugin installation should either provide such a helper script/application or use the ./configure option --with-install-plugins-helper=/path/to/installer to make GStreamer call an installer of their own directly.

It is strongly recommended that vendors provide a small helper application as interlocutor to the real installer though, even more so if command line argument munging is required to transform the command line arguments passed by GStreamer to the helper application into arguments that are understood by the reeal installer.

The helper application path defined at compile time can be overriden at runtime by setting the GST_INSTALL_PLUGINS_HELPER environment variable. This can be useful for testing/debugging purposes.

2. Arguments passed to the install helper

GStreamer will pass the following arguments to the install helper (this is in addition to the path of the executable itself, which is by convention argv[0]):

3. Detail string describing the missing plugin

The string is in UTF-8 encoding and is made up of several fields, separated by '|' characters (but neither the first nor the last character is a '|'). The fields are:

An entire ID string might then look like this, for example: gstreamer|0.10|totem|Vorbis audio decoder|decoder-audio/x-vorbis

Plugin installers parsing this ID string should expect further fields also separated by '|' symbols and either ignore them, warn the user, or error out when encountering them.

Those unfamiliar with the GStreamer 'caps' system should note a few things about the caps string used in the above decoder/encoder case:

4. Exit codes the installer should return

The installer should return one of the following exit codes when it exits:

5. How to map the required detail string to packages

It is up to the vendor to find mechanism to map required components from the detail string to the actual packages/plugins to install. This could be a hardcoded list of mappings, for example, or be part of the packaging system metadata.

GStreamer plugin files can be introspected for this information. The gst-inspect utility has a special command line option that will output information similar to what is required. For example $ gst-inspect-0.10 --print-plugin-auto-install-info /path/to/libgstvorbis.so should output something along the lines of decoder-audio/x-vorbis element-vorbisdec element-vorbisenc element-vorbisparse element-vorbistag encoder-audio/x-vorbis Note that in the encoder and decoder case the introspected caps can be more complex with additional fields, e.g. audio/mpeg,mpegversion=(int){2,4}, so they will not always exactly match the caps wanted by the application. It is up to the installer to deal with this (either by doing proper caps intersection using the GStreamer GstCaps API, or by only taking into account the media type).

Another potential source of problems are plugins such as ladspa or libvisual where the list of elements depends on the installed ladspa/libvisual plugins at the time. This is also up to the distribution to handle (but usually not relevant for playback applications).

enum GstInstallPluginsReturn

typedef enum {
  /* Return codes from the installer. Returned by gst_install_plugins_sync(),
   * or passed as result code to your #GstInstallPluginsResultFunc */
  GST_INSTALL_PLUGINS_SUCCESS = 0,
  GST_INSTALL_PLUGINS_NOT_FOUND = 1,
  GST_INSTALL_PLUGINS_ERROR = 2,
  GST_INSTALL_PLUGINS_PARTIAL_SUCCESS = 3,
  GST_INSTALL_PLUGINS_USER_ABORT = 4,

  /* Returned by gst_install_plugins_sync(), or passed as result code to your
   * #GstInstallPluginsResultFunc */
  GST_INSTALL_PLUGINS_CRASHED = 100,
  GST_INSTALL_PLUGINS_INVALID,

  /* Return codes from starting the external helper, may be returned by both
   * gst_install_plugins_sync() and gst_install_plugins_async(), but should
   * never be seen by a #GstInstallPluginsResultFunc */
  GST_INSTALL_PLUGINS_STARTED_OK = 200,
  GST_INSTALL_PLUGINS_INTERNAL_FAILURE,
  GST_INSTALL_PLUGINS_HELPER_MISSING,
  GST_INSTALL_PLUGINS_INSTALL_IN_PROGRESS
} GstInstallPluginsReturn;

Result codes returned by gst_install_plugins_async() and gst_install_plugins_sync(), and also the result code passed to the GstInstallPluginsResultFunc specified with gst_install_plugin_async().

These codes indicate success or failure of starting an external installer program and to what extent the requested plugins could be installed.

Since 0.10.12

GstInstallPluginsResultFunc ()

void                (*GstInstallPluginsResultFunc)      (GstInstallPluginsReturn result,
                                                         gpointer user_data);

The prototype of the callback function that will be called once the external plugin installer program has returned. You only need to provide a callback function if you are using the asynchronous interface.

Since 0.10.12

gst_install_plugins_async ()

GstInstallPluginsReturn gst_install_plugins_async       (gchar **details,
                                                         GstInstallPluginsContext *ctx,
                                                         GstInstallPluginsResultFunc func,
                                                         gpointer user_data);

Requests plugin installation without blocking. Once the plugins have been installed or installation has failed, func will be called with the result of the installation and your provided user_data pointer.

This function requires a running GLib/Gtk main loop. If you are not running a GLib/Gtk main loop, make sure to regularly call g_main_context_iteration(NULL,FALSE).

The installer strings that make up detail are typically obtained by calling gst_missing_plugin_message_get_installer_detail() on missing-plugin messages that have been caught on a pipeline's bus or created by the application via the provided API, such as gst_missing_element_message_new().

It is possible to request the installation of multiple missing plugins in one go (as might be required if there is a demuxer for a certain format installed but no suitable video decoder and no suitable audio decoder).

Since 0.10.12

gst_install_plugins_sync ()

GstInstallPluginsReturn gst_install_plugins_sync        (gchar **details,
                                                         GstInstallPluginsContext *ctx);

Requests plugin installation and block until the plugins have been installed or installation has failed.

This function should almost never be used, it only exists for cases where a non-GLib main loop is running and the user wants to run it in a separate thread and marshal the result back asynchronously into the main thread using the other non-GLib main loop. You should almost always use gst_install_plugins_async() instead of this function.

Since 0.10.12

gst_install_plugins_return_get_name ()

const gchar*        gst_install_plugins_return_get_name (GstInstallPluginsReturn ret);

Convenience function to return the descriptive string associated with a status code. This function returns English strings and should not be used for user messages. It is here only to assist in debugging.

Since 0.10.12

gst_install_plugins_installation_in_progress ()

gboolean            gst_install_plugins_installation_in_progress
                                                        (void);

Checks whether plugin installation (initiated by this application only) is currently in progress.

Since 0.10.12

gst_install_plugins_supported ()

gboolean            gst_install_plugins_supported       (void);

Checks whether plugin installation is likely to be supported by the current environment. This currently only checks whether the helper script that is to be provided by the distribution or operating system vendor exists.

Since 0.10.15

GstInstallPluginsContext

typedef struct _GstInstallPluginsContext GstInstallPluginsContext;

Opaque context structure for the plugin installation. Use the provided API to set details on it.

Since 0.10.12

gst_install_plugins_context_new ()

GstInstallPluginsContext* gst_install_plugins_context_new
                                                        (void);

Creates a new GstInstallPluginsContext.

Since 0.10.12

gst_install_plugins_context_free ()

void                gst_install_plugins_context_free    (GstInstallPluginsContext *ctx);

Frees a GstInstallPluginsContext.

Since 0.10.12

gst_install_plugins_context_set_xid ()

void                gst_install_plugins_context_set_xid (GstInstallPluginsContext *ctx,
                                                         guint xid);

This function is for X11-based applications (such as most Gtk/Qt applications on linux/unix) only. You can use it to tell the external the XID of your main application window, so the installer can make its own window transient to your application windonw during the installation.

If set, the XID will be passed to the installer via a --transient-for=XID command line option.

Gtk+/Gnome application should be able to obtain the XID of the top-level window like this:

##include <gtk/gtk.h>
##ifdef GDK_WINDOWING_X11
##include <gdk/gdkx.h>
##endif
...
##ifdef GDK_WINDOWING_X11
  xid = GDK_WINDOW_XWINDOW (GTK_WIDGET (application_window)->window);
##endif
...

Since 0.10.12