mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-09-08 13:18:52 +00:00
MIME-type -> media types Fix up the manual in various places with the 1.0 way of doing things such as probes, static elements, scheduling, ... Add porting from 0.10 to 1.0 chapter. Add probe example to build. Remove some docs for remove components such as GstMixer and GstPropertyProbe, XML...
376 lines
11 KiB
XML
376 lines
11 KiB
XML
<chapter id="chapter-components">
|
|
<title>Components</title>
|
|
|
|
<para>
|
|
&GStreamer; includes several higher-level components to simplify an
|
|
application developer's life. All of the components discussed here (for now) are
|
|
targetted at media playback. The idea of each of these components is
|
|
to integrate as closely as possible with a &GStreamer; pipeline, but
|
|
to hide the complexity of media type detection and several other
|
|
rather complex topics that have been discussed in <xref
|
|
linkend="part-advanced"/>.
|
|
</para>
|
|
|
|
<para>
|
|
We currently recommend people to use either playbin (see <xref
|
|
linkend="section-components-playbin"/>) or decodebin (see <xref
|
|
linkend="section-components-decodebin"/>), depending on their needs.
|
|
Playbin is the recommended solution for everything related to simple
|
|
playback of media that should just work. Decodebin is a more flexible
|
|
autoplugger that could be used to add more advanced features, such
|
|
as playlist support, crossfading of audio tracks and so on. Its
|
|
programming interface is more low-level than that of playbin, though.
|
|
</para>
|
|
|
|
<sect1 id="section-components-playbin">
|
|
<title>Playbin</title>
|
|
|
|
<para>
|
|
Playbin is an element that can be created using the standard &GStreamer;
|
|
API (e.g. <function>gst_element_factory_make ()</function>). The factory
|
|
is conveniently called <quote>playbin</quote>. By being a
|
|
<classname>GstPipeline</classname> (and thus a
|
|
<classname>GstElement</classname>), playbin automatically supports all
|
|
of the features of this class, including error handling, tag support,
|
|
state handling, getting stream positions, seeking, and so on.
|
|
</para>
|
|
|
|
<para>
|
|
Setting up a playbin pipeline is as simple as creating an instance of
|
|
the playbin element, setting a file location using the
|
|
<quote>uri</quote> property on playbin, and then setting the element
|
|
to the <classname>GST_STATE_PLAYING</classname> state (the location has to be a valid
|
|
URI, so <quote><protocol>://<location></quote>, e.g.
|
|
file:///tmp/my.ogg or http://www.example.org/stream.ogg). Internally,
|
|
playbin will set up a pipeline to playback the media location.
|
|
</para>
|
|
|
|
<programlisting><!-- example-begin playbin.c a -->
|
|
#include <gst/gst.h>
|
|
<!-- example-end playbin.c a -->
|
|
[.. my_bus_callback goes here ..]<!-- example-begin playbin.c b --><!--
|
|
static gboolean
|
|
my_bus_callback (GstBus *bus,
|
|
GstMessage *message,
|
|
gpointer data)
|
|
{
|
|
GMainLoop *loop = data;
|
|
|
|
switch (GST_MESSAGE_TYPE (message)) {
|
|
case GST_MESSAGE_ERROR: {
|
|
GError *err;
|
|
gchar *debug;
|
|
|
|
gst_message_parse_error (message, &err, &debug);
|
|
g_print ("Error: %s\n", err->message);
|
|
g_error_free (err);
|
|
g_free (debug);
|
|
|
|
g_main_loop_quit (loop);
|
|
break;
|
|
}
|
|
case GST_MESSAGE_EOS:
|
|
/* end-of-stream */
|
|
g_main_loop_quit (loop);
|
|
break;
|
|
default:
|
|
/* unhandled message */
|
|
break;
|
|
}
|
|
|
|
/* remove message from the queue */
|
|
return TRUE;
|
|
}
|
|
--><!-- example-end playbin.c b -->
|
|
<!-- example-begin playbin.c c -->
|
|
gint
|
|
main (gint argc,
|
|
gchar *argv[])
|
|
{
|
|
GMainLoop *loop;
|
|
GstElement *play;
|
|
GstBus *bus;
|
|
|
|
/* init GStreamer */
|
|
gst_init (&argc, &argv);
|
|
loop = g_main_loop_new (NULL, FALSE);
|
|
|
|
/* make sure we have a URI */
|
|
if (argc != 2) {
|
|
g_print ("Usage: %s <URI>\n", argv[0]);
|
|
return -1;
|
|
}
|
|
|
|
/* set up */
|
|
play = gst_element_factory_make ("playbin", "play");
|
|
g_object_set (G_OBJECT (play), "uri", argv[1], NULL);
|
|
|
|
bus = gst_pipeline_get_bus (GST_PIPELINE (play));
|
|
gst_bus_add_watch (bus, my_bus_callback, loop);
|
|
gst_object_unref (bus);
|
|
|
|
gst_element_set_state (play, GST_STATE_PLAYING);
|
|
|
|
/* now run */
|
|
g_main_loop_run (loop);
|
|
|
|
/* also clean up */
|
|
gst_element_set_state (play, GST_STATE_NULL);
|
|
gst_object_unref (GST_OBJECT (play));
|
|
|
|
return 0;
|
|
}
|
|
<!-- example-end playbin.c c --></programlisting>
|
|
|
|
<para>
|
|
Playbin has several features that have been discussed previously:
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
Settable video and audio output (using the <quote>video-sink</quote>
|
|
and <quote>audio-sink</quote> properties).
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Mostly controllable and trackable as a
|
|
<classname>GstElement</classname>, including error handling, eos
|
|
handling, tag handling, state handling (through the
|
|
<classname>GstBus</classname>), media position handling and
|
|
seeking.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Buffers network-sources, with buffer fullness notifications being
|
|
passed through the <classname>GstBus</classname>.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Supports visualizations for audio-only media.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Supports subtitles, both in the media as well as from separate
|
|
files. For separate subtitle files, use the <quote>suburi</quote>
|
|
property.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Supports stream selection and disabling. If your media has
|
|
multiple audio or subtitle tracks, you can dynamically choose
|
|
which one to play back, or decide to turn it off altogether
|
|
(which is especially useful to turn off subtitles). For each
|
|
of those, use the <quote>current-text</quote> and other related
|
|
properties.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<para>
|
|
For convenience, it is possible to test <quote>playbin</quote> on
|
|
the commandline, using the command <quote>gst-launch-1.0 playbin
|
|
uri=file:///path/to/file</quote>.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="section-components-decodebin">
|
|
<title>Decodebin</title>
|
|
|
|
<para>
|
|
Decodebin is the actual autoplugger backend of playbin, which was
|
|
discussed in the previous section. Decodebin will, in short, accept
|
|
input from a source that is linked to its sinkpad and will try to
|
|
detect the media type contained in the stream, and set up decoder
|
|
routines for each of those. It will automatically select decoders.
|
|
For each decoded stream, it will emit the <quote>pad-added</quote>
|
|
signal, to let the client know about the newly found decoded stream.
|
|
For unknown streams (which might be the whole stream), it will emit
|
|
the <quote>unknown-type</quote> signal. The application is then
|
|
responsible for reporting the error to the user.
|
|
</para>
|
|
<programlisting><!-- example-begin decodebin.c a -->
|
|
#include <gst/gst.h>
|
|
<!-- example-end decodebin.c a -->
|
|
[.. my_bus_callback goes here ..]<!-- example-begin decodebin.c b --><!--
|
|
static gboolean
|
|
my_bus_callback (GstBus *bus,
|
|
GstMessage *message,
|
|
gpointer data)
|
|
{
|
|
GMainLoop *loop = data;
|
|
|
|
switch (GST_MESSAGE_TYPE (message)) {
|
|
case GST_MESSAGE_ERROR: {
|
|
GError *err;
|
|
gchar *debug;
|
|
|
|
gst_message_parse_error (message, &err, &debug);
|
|
g_print ("Error: %s\n", err->message);
|
|
g_error_free (err);
|
|
g_free (debug);
|
|
|
|
g_main_loop_quit (loop);
|
|
break;
|
|
}
|
|
case GST_MESSAGE_EOS:
|
|
/* end-of-stream */
|
|
g_main_loop_quit (loop);
|
|
break;
|
|
default:
|
|
/* unhandled message */
|
|
break;
|
|
}
|
|
|
|
/* remove message from the queue */
|
|
return TRUE;
|
|
}
|
|
--><!-- example-end decodebin.c b -->
|
|
<!-- example-begin decodebin.c c -->
|
|
GstElement *pipeline, *audio;
|
|
|
|
static void
|
|
cb_newpad (GstElement *decodebin,
|
|
GstPad *pad,
|
|
gpointer data)
|
|
{
|
|
GstCaps *caps;
|
|
GstStructure *str;
|
|
GstPad *audiopad;
|
|
|
|
/* only link once */
|
|
audiopad = gst_element_get_static_pad (audio, "sink");
|
|
if (GST_PAD_IS_LINKED (audiopad)) {
|
|
g_object_unref (audiopad);
|
|
return;
|
|
}
|
|
|
|
/* check media type */
|
|
caps = gst_pad_query_caps (pad, NULL);
|
|
str = gst_caps_get_structure (caps, 0);
|
|
if (!g_strrstr (gst_structure_get_name (str), "audio")) {
|
|
gst_caps_unref (caps);
|
|
gst_object_unref (audiopad);
|
|
return;
|
|
}
|
|
gst_caps_unref (caps);
|
|
|
|
/* link'n'play */
|
|
gst_pad_link (pad, audiopad);
|
|
|
|
g_object_unref (audiopad);
|
|
}
|
|
|
|
gint
|
|
main (gint argc,
|
|
gchar *argv[])
|
|
{
|
|
GMainLoop *loop;
|
|
GstElement *src, *dec, *conv, *sink;
|
|
GstPad *audiopad;
|
|
GstBus *bus;
|
|
|
|
/* init GStreamer */
|
|
gst_init (&argc, &argv);
|
|
loop = g_main_loop_new (NULL, FALSE);
|
|
|
|
/* make sure we have input */
|
|
if (argc != 2) {
|
|
g_print ("Usage: %s <filename>\n", argv[0]);
|
|
return -1;
|
|
}
|
|
|
|
/* setup */
|
|
pipeline = gst_pipeline_new ("pipeline");
|
|
|
|
bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
|
|
gst_bus_add_watch (bus, my_bus_callback, loop);
|
|
gst_object_unref (bus);
|
|
|
|
src = gst_element_factory_make ("filesrc", "source");
|
|
g_object_set (G_OBJECT (src), "location", argv[1], NULL);
|
|
dec = gst_element_factory_make ("decodebin", "decoder");
|
|
g_signal_connect (dec, "pad-added", G_CALLBACK (cb_newpad), NULL);
|
|
gst_bin_add_many (GST_BIN (pipeline), src, dec, NULL);
|
|
gst_element_link (src, dec);
|
|
|
|
/* create audio output */
|
|
audio = gst_bin_new ("audiobin");
|
|
conv = gst_element_factory_make ("audioconvert", "aconv");
|
|
audiopad = gst_element_get_static_pad (conv, "sink");
|
|
sink = gst_element_factory_make ("alsasink", "sink");
|
|
gst_bin_add_many (GST_BIN (audio), conv, sink, NULL);
|
|
gst_element_link (conv, sink);
|
|
gst_element_add_pad (audio,
|
|
gst_ghost_pad_new ("sink", audiopad));
|
|
gst_object_unref (audiopad);
|
|
gst_bin_add (GST_BIN (pipeline), audio);
|
|
|
|
/* run */
|
|
gst_element_set_state (pipeline, GST_STATE_PLAYING);
|
|
g_main_loop_run (loop);
|
|
|
|
/* cleanup */
|
|
gst_element_set_state (pipeline, GST_STATE_NULL);
|
|
gst_object_unref (GST_OBJECT (pipeline));
|
|
|
|
return 0;
|
|
}
|
|
<!-- example-end decodebin.c c --></programlisting>
|
|
|
|
<para>
|
|
Decodebin, similar to playbin, supports the following features:
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
Can decode an unlimited number of contained streams to decoded
|
|
output pads.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Is handled as a <classname>GstElement</classname> in all ways,
|
|
including tag or error forwarding and state handling.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<para>
|
|
Although decodebin is a good autoplugger, there's a whole lot of
|
|
things that it does not do and is not intended to do:
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
Taking care of input streams with a known media type (e.g. a DVD,
|
|
an audio-CD or such).
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Selection of streams (e.g. which audio track to play in case of
|
|
multi-language media streams).
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Overlaying subtitles over a decoded video stream.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<para>
|
|
Decodebin can be easily tested on the commandline, e.g. by using the
|
|
command <command>gst-launch-1.0 filesrc location=file.ogg ! decodebin
|
|
! audioconvert ! audioresample ! autoaudiosink</command>.
|
|
</para>
|
|
<para>
|
|
The uridecodebin element is very similar to decodebin, only that it
|
|
automatically plugs a source plugin based on the protocol of the URI
|
|
given.
|
|
</para>
|
|
</sect1>
|
|
|
|
</chapter>
|