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<tr><td colspan="5" class="shortcuts"><nobr><a href="#id2587143" class="shortcut">Top</a>
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<a href="#id2592931" class="shortcut">Description</a></nobr></td></tr>
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<div class="refentry" lang="en">
<a name="gst-plugins-base-plugins-playbin"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
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<h2>
<a name="id2587143"></a><span class="refentrytitle">playbin</span>
</h2>
<p>playbin — Autoplug and play media from an uri</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<pre class="synopsis">
</pre>
</div>
<div class="refsect1" lang="en">
<a name="id2592931"></a><h2>Description</h2>
<p>
</p>
<div class="refsect2" lang="en">
<a name="id2574351"></a><p>
Playbin provides a stand-alone everything-in-one abstraction for an
audio and/or video player.
</p>
<p>
It can handle both audio and video files and features
</p>
<div class="itemizedlist"><ul type="disc">
<li>
automatic file type recognition and based on that automatic
selection and usage of the right audio/video/subtitle demuxers/decoders
</li>
<li>
visualisations for audio files
</li>
<li>
subtitle support for video files
</li>
<li>
stream selection between different audio/subtitles streams
</li>
<li>
meta info (tag) extraction
</li>
<li>
easy access to the last video frame
</li>
<li>
buffering when playing streams over a network
</li>
<li>
volume control
</li>
</ul></div>
<p>
</p>
<h3>Usage</h3>
<p>
A playbin element can be created just like any other element using
<code class="function">gst_element_factory_make()</code>. The file/URI to play should be set via the "uri"
property. This must be an absolute URI, relative file paths are not allowed.
Example URIs are file:///home/joe/movie.avi or http://www.joedoe.com/foo.ogg
</p>
<p>
Playbin is a <span class="type">GstPipeline</span>. It will notify the application of everything
that's happening (errors, end of stream, tags found, state changes, etc.)
by posting messages on its <span class="type">GstBus</span>. The application needs to watch the
bus.
</p>
<p>
Playback can be initiated by setting the element to PLAYING state using
<code class="function">gst_element_set_state()</code>. Note that the state change will take place in
the background in a separate thread, when the function returns playback
is probably not happening yet and any errors might not have occured yet.
Applications using playbin should ideally be written to deal with things
completely asynchroneous.
</p>
<p>
When playback has finished (an EOS message has been received on the bus)
or an error has occured (an ERROR message has been received on the bus) or
the user wants to play a different track, playbin should be set back to
READY or NULL state, then the "uri" property should be set to the new
location and then playbin be set to PLAYING state again.
</p>
<p>
Seeking can be done using <code class="function">gst_element_seek_simple()</code> or <code class="function">gst_element_seek()</code>
on the playbin element. Again, the seek will not be executed
instantaneously, but will be done in a background thread. When the seek
call returns the seek will most likely still be in process. An application
may wait for the seek to finish (or fail) using <code class="function">gst_element_get_state()</code> with
-1 as the timeout, but this will block the user interface and is not
recommended at all.
</p>
<p>
Applications may query the current position and duration of the stream
via <code class="function">gst_element_query_position()</code> and <code class="function">gst_element_query_duration()</code> and
setting the format passed to GST_FORMAT_TIME. If the query was successful,
the duration or position will have been returned in units of nanoseconds.
</p>
<h3>Advanced Usage: specifying the audio and video sink</h3>
<p>
By default, if no audio sink or video sink has been specified via the
"audio-sink" or "video-sink" property, playbin will use the autoaudiosink
and autovideosink elements to find the first-best available output method.
This should work in most cases, but is not always desirable. Often either
the user or application might want to specify more explicitly what to use
for audio and video output.
</p>
<p>
If the application wants more control over how audio or video should be
output, it may create the audio/video sink elements itself (for example
using <code class="function">gst_element_factory_make()</code>) and provide them to playbin using the
"audio-sink" or "video-sink" property.
</p>
<p>
GNOME-based applications, for example, will usually want to create
gconfaudiosink and gconfvideosink elements and make playbin use those,
so that output happens to whatever the user has configured in the GNOME
Multimedia System Selector confinguration dialog.
</p>
<p>
The sink elements do not necessarily need to be ready-made sinks. It is
possible to create container elements that look like a sink to playbin,
but in reality contain a number of custom elements linked together. This
can be achieved by creating a <span class="type">GstBin</span> and putting elements in there and
linking them, and then creating a sink <span class="type">GstGhostPad</span> for the bin and pointing
it to the sink pad of the first element within the bin. This can be used
for a number of purposes, for example to force output to a particular
format or to modify or observe the data before it is output.
</p>
<p>
It is also possible to 'suppress' audio and/or video output by using
'fakesink' elements (or capture it from there using the fakesink element's
"handoff" signal, which, nota bene, is fired from the streaming thread!).
</p>
<h3>Retrieving Tags and Other Meta Data</h3>
<p>
Most of the common meta data (artist, title, etc.) can be retrieved by
watching for TAG messages on the pipeline's bus (see above).
</p>
<p>
Other more specific meta information like width/height/framerate of video
streams or samplerate/number of channels of audio streams can be obtained
using the "stream-info" property, which will return a GList of stream info
objects, one for each stream. These are opaque objects that can only be
accessed via the standard GObject property interface, ie. <code class="function">g_object_get()</code>.
Each stream info object has the following properties:
</p>
<div class="itemizedlist"><ul type="disc">
<li>"object" (GstObject) (the decoder source pad usually)</li>
<li>"type" (enum) (if this is an audio/video/subtitle stream)</li>
<li>"decoder" (string) (name of decoder used to decode this stream)</li>
<li>"mute" (boolean) (to mute or unmute this stream)</li>
<li>"caps" (GstCaps) (caps of the decoded stream)</li>
<li>"language-code" (string) (ISO-639 language code for this stream, mostly used for audio/subtitle streams)</li>
<li>"codec" (string) (format this stream was encoded in)</li>
</ul></div>
<p>
Stream information from the stream-info properties is best queried once
playbin has changed into PAUSED or PLAYING state (which can be detected
via a state-changed message on the bus where old_state=READY and
new_state=PAUSED), since before that the list might not be complete yet or
not contain all available information (like language-codes).
</p>
<h3>Buffering</h3>
<p>
Playbin handles buffering automatically for the most part, but applications
need to handle parts of the buffering process as well. Whenever playbin is
buffering, it will post BUFFERING messages on the bus with a percentage
value that shows the progress of the buffering process. Applications need
to set playbin to PLAYING or PAUSED state in response to these messages.
They may also want to convey the buffering progress to the user in some
way. Here is how to extract the percentage information from the message
(requires GStreamer >= 0.10.11):
</p>
<p>
</p>
<pre class="programlisting">
switch (GST_MESSAGE_TYPE (msg)) {
case GST_MESSAGE_BUFFERING: {
gint percent = 0;
gst_message_parse_buffering (msg, &percent);
g_print ("Buffering (%%u percent done)", percent);
break;
}
...
}
</pre>
<p>
Note that applications should keep/set the pipeline in the PAUSED state when
a BUFFERING message is received with a buffer percent value < 100 and set
the pipeline back to PLAYING state when a BUFFERING message with a value
of 100 percent is received (if PLAYING is the desired state, that is).
</p>
<h3>Embedding the video window in your application</h3>
<p>
By default, playbin (or rather the video sinks used) will create their own
window. Applications will usually want to force output to a window of their
own, however. This can be done using the GstXOverlay interface, which most
video sinks implement. See the documentation there for more details.
</p>
<h3>Specifying which CD/DVD device to use</h3>
<p>
The device to use for CDs/DVDs needs to be set on the source element
playbin creates before it is opened. The only way to do this at the moment
is to connect to playbin's "notify::source" signal, which will be emitted
by playbin when it has created the source element for a particular URI.
In the signal callback you can check if the source element has a "device"
property and set it appropriately. In future ways might be added to specify
the device as part of the URI, but at the time of writing this is not
possible yet.
</p>
<h3>Examples</h3>
<p>
Here is a simple pipeline to play back a video or audio file:
</p>
<pre class="programlisting">
gst-launch -v playbin uri=file:///path/to/somefile.avi
</pre>
<p>
This will play back the given AVI video file, given that the video and
audio decoders required to decode the content are installed. Since no
special audio sink or video sink is supplied (not possible via gst-launch),
playbin will try to find a suitable audio and video sink automatically
using the autoaudiosink and autovideosink elements.
</p>
<p>
Here is a another pipeline to play track 4 of an audio CD:
</p>
<pre class="programlisting">
gst-launch -v playbin uri=cdda://4
</pre>
<p>
This will play back track 4 on an audio CD in your disc drive (assuming
the drive is detected automatically by the plugin).
</p>
<p>
Here is a another pipeline to play title 1 of a DVD:
</p>
<pre class="programlisting">
gst-launch -v playbin uri=dvd://1
</pre>
<p>
This will play back title 1 of a DVD in your disc drive (assuming
the drive is detected automatically by the plugin).
</p>
</div>
<div class="refsect2" lang="en">
<a name="id2608145"></a><h3>Element Information</h3>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><span class="term">plugin</span></td>
<td>
<a href="gst-plugins-base-plugins-plugin-playbin.html#plugin-playbin">playbin</a>
</td>
</tr>
<tr>
<td><span class="term">author</span></td>
<td>Wim Taymans <wim@fluendo.com></td>
</tr>
<tr>
<td><span class="term">class</span></td>
<td>Generic/Bin/Player</td>
</tr>
</tbody>
</table></div>
<h3>Element Pads</h3>
</div>
<p>
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2608550"></a><h2>Details</h2>
</div>
</div>
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