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Functions
Description
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
when the application itself has found that it wants or needs to install a certain element
when the application has been notified by an element (such as playbin or decodebin) that one or more plugins are missing *and* the application has decided that it wants to install one or more of those missing plugins
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()
.
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.
A Gtk/GLib main loop must be running in order for the result function to be called when the external installer has finished. If this is not the case, make sure to regularly call in your code:
g_main_context_iteration (NULL,FALSE);
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 real 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]):
none to many optional arguments in the form of
--foo-bar=val
. Example:--transient-for=XID
where XID is the X Window ID of the main window of the calling application (so the installer can make itself transient to that window). Unknown optional arguments should be ignored by the installer.one 'installer detail string' argument for each plugin to be installed; these strings will have a
gstreamer
prefix; the exact format of the detail string is explained below
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:
plugin system identifier, ie. "gstreamer" This identifier determines the format of the rest of the detail string. Automatic plugin installers should not process detail strings with unknown identifiers. This allows other plugin-based libraries to use the same mechanism for their automatic plugin installation needs, or for the format to be changed should it turn out to be insufficient.
plugin system version, e.g. "0.10" This is required so that when there is a GStreamer-0.12 or GStreamer-1.0 at some point in future, the different major versions can still co-exist and use the same plugin install mechanism in the same way.
application identifier, e.g. "totem" This may also be in the form of "pid/12345" if the program name can't be obtained for some reason.
human-readable localised description of the required component, e.g. "Vorbis audio decoder"
-
identifier string for the required component (see below for details about how to map this to the package/plugin that needs installing), e.g.
urisource-$(PROTOCOL_REQUIRED), e.g. urisource-http or urisource-mms
element-$(ELEMENT_REQUIRED), e.g. element-videoconvert
-
decoder-$(CAPS_REQUIRED), e.g. (do read below for more details!):
decoder-audio/x-vorbis
decoder-application/ogg
decoder-audio/mpeg, mpegversion=(int)4
decoder-video/mpeg, systemstream=(boolean)true, mpegversion=(int)2
encoder-$(CAPS_REQUIRED), e.g. encoder-audio/x-vorbis
optional further fields not yet specified
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:
the first part ("video/mpeg") of the caps string is a GStreamer media type and *not* a MIME type. Wherever possible, the GStreamer media type will be the same as the corresponding MIME type, but often it is not.
a caps string may or may not have additional comma-separated fields of various types (as seen in the examples above)
-
the caps string of a 'required' component (as above) will always have fields with fixed values, whereas an introspected string (see below) may have fields with non-fixed values. Compare for example:
audio/mpeg, mpegversion=(int)4
vs.audio/mpeg, mpegversion=(int){2, 4}
video/mpeg, mpegversion=(int)2
vs.video/mpeg, systemstream=(boolean){ true, false}, mpegversion=(int)[1, 2]
4. Exit codes the installer should return
The installer should return one of the following exit codes when it exits:
0 if all of the requested plugins could be installed (GST_INSTALL_PLUGINS_SUCCESS)
1 if no appropriate installation candidate for any of the requested plugins could be found. Only return this if nothing has been installed (GST_INSTALL_PLUGINS_NOT_FOUND)
2 if an error occured during the installation. The application will assume that the user will already have seen an error message by the installer in this case and will usually not show another one (GST_INSTALL_PLUGINS_ERROR)
3 if some of the requested plugins could be installed, but not all (GST_INSTALL_PLUGINS_PARTIAL_SUCCESS)
4 if the user aborted the installation (GST_INSTALL_PLUGINS_USER_ABORT)
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-1.0 --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).
Functions
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.
Parameters
result |
whether the installation of the requested plugins succeeded or not |
|
user_data |
the user data passed to |
gst_install_plugins_async ()
GstInstallPluginsReturn gst_install_plugins_async (const gchar * const *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).
Parameters
details |
NULL-terminated array of installer string details (see below). |
[array zero-terminated=1][transfer none] |
ctx |
a GstInstallPluginsContext, or NULL. |
[allow-none] |
func |
the function to call when the installer program returns. |
[scope async] |
user_data |
the user data to pass to |
[closure] |
gst_install_plugins_sync ()
GstInstallPluginsReturn gst_install_plugins_sync (const gchar * const *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.
Parameters
details |
NULL-terminated array of installer string details. |
[array zero-terminated=1][transfer none] |
ctx |
a GstInstallPluginsContext, or NULL. |
[allow-none] |
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.
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.
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.
gst_install_plugins_context_new ()
GstInstallPluginsContext *
gst_install_plugins_context_new (void
);
Creates a new GstInstallPluginsContext.
Returns
a new GstInstallPluginsContext. Free with
gst_install_plugins_context_free()
when no longer needed
gst_install_plugins_context_free ()
void
gst_install_plugins_context_free (GstInstallPluginsContext *ctx
);
Frees a GstInstallPluginsContext.
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 installer the XID of your main application window. That way the installer can make its own window transient to your application window 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:
1 2 3 4 5 6 7 8 9 |
##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 ... |
gst_install_plugins_context_set_confirm_search ()
void gst_install_plugins_context_set_confirm_search (GstInstallPluginsContext *ctx
,gboolean confirm_search
);
This function is used to tell the external installer process whether it should ask for confirmation or not before searching for missing plugins.
If set, this option will be passed to the installer via a --interaction=[show-confirm-search|hide-confirm-search] command line option.
Since: 1.6
gst_install_plugins_context_set_desktop_id ()
void gst_install_plugins_context_set_desktop_id (GstInstallPluginsContext *ctx
,const gchar *desktop_id
);
This function is used to pass the calling application's desktop file ID to the external installer process.
A desktop file ID is the basename of the desktop file, including the .desktop extension.
If set, the desktop file ID will be passed to the installer via a --desktop-id= command line option.
Since: 1.6
gst_install_plugins_context_set_startup_notification_id ()
void gst_install_plugins_context_set_startup_notification_id (GstInstallPluginsContext *ctx
,const gchar *startup_id
);
Sets the startup notification ID for the launched process.
This is typically used to to pass the current X11 event timestamp to the external installer process.
Startup notification IDs are defined in the FreeDesktop.Org Startup Notifications standard.
If set, the ID will be passed to the installer via a --startup-notification-id= command line option.
GTK+/GNOME applications should be able to create a startup notification ID like this:
1 2 3 |
timestamp = gtk_get_current_event_time (); startup_id = g_strdup_printf ("_TIME%u", timestamp); ... |
Since: 1.6
Types and Values
enum 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_plugins_async()
.
These codes indicate success or failure of starting an external installer program and to what extent the requested plugins could be installed.
Members
all of the requested plugins could be installed |
||
no appropriate installation candidate for any of the requested plugins could be found. Only return this if nothing has been installed. Return GST_INSTALL_PLUGINS_PARTIAL_SUCCESS if some (but not all) of the requested plugins could be installed. |
||
an error occured during the installation. If this happens, the user has already seen an error message and another one should not be displayed |
||
some of the requested plugins could be installed, but not all |
||
the user has aborted the installation |
||
the installer had an unclean exit code (ie. death by signal) |
||
the helper returned an invalid status code |
||
returned by |
||
some internal failure has occured when trying to start the installer |
||
the helper script to call the actual installer is not installed |
||
a previously-started plugin installation is still in progress, try again later |