mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-12-17 05:46:36 +00:00
018a6f381b
Original commit message from CVS: First draft of Chapter 1 (introduction) and Chapter 2 (basic concepts) of the GStreamer manual.
104 lines
3.5 KiB
Text
104 lines
3.5 KiB
Text
<chapter id="cha-states">
|
|
<title>Element states</title>
|
|
<para>
|
|
One you have created a pipeline packed with elements, nothing will happen yet.
|
|
This is where the different states come into play.
|
|
</para>
|
|
|
|
<sect1 id="sec-states">
|
|
<title>The different element states</title>
|
|
<para>
|
|
All elements can be in one of the following four states:
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
NULL: this is the default state all elements are in when they are created
|
|
and are doing nothing.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
READY: An element is ready to start doing something.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
PLAYING: The element is doing something.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
PAUSED: The element is paused for a period of time.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
All elements start with the NULL state. The elements will go throught the following state changes:
|
|
<figure float="1" id="sec-state-img">
|
|
<title>The different states of a <classname>GstElement</classname> and the state transitions</title>
|
|
<graphic fileref="images/state-diagram" format="png"></graphic>
|
|
</figure>
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sec-states-null">
|
|
<title>The NULL state</title>
|
|
<para>
|
|
When you created the pipeline all of the elements will be in the NULL state. There is
|
|
nothing spectacular about the NULL state.
|
|
</para>
|
|
<note>
|
|
<para>
|
|
Don't forget to reset the pipeline to the NULL state when you are not going to use it
|
|
anymore. This will allow the elements to free the resources they might use.
|
|
</para>
|
|
</note>
|
|
</sect1>
|
|
|
|
<sect1 id="sec-states-ready">
|
|
<title>The READY state</title>
|
|
<para>
|
|
You will start the pipeline by first setting it to the READY state. This will allow the
|
|
pipeline and all the elements contained in it to prepare themselves for the actions
|
|
they are about to perform.
|
|
</para>
|
|
<para>
|
|
The typical actions that an element will perform in the READY state might be to open a file or
|
|
an audio device. Some more complex elements might have a non trivial action to perform in
|
|
the READY state such as connecting to a media server using a CORBA connection.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sec-states-playing">
|
|
<title>The PLAYING state</title>
|
|
<para>
|
|
A Pipeline that is in the READY state can be started by setting it to the PLAYING state. At
|
|
that time data will start to flow all the way through the pipeline.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sec-states-paused">
|
|
<title>The PAUSED state</title>
|
|
<para>
|
|
A pipeline that is playing can be set to the PAUSED state. This will temporarily stop all
|
|
data flowing through the pipeline.
|
|
</para>
|
|
<para>
|
|
You can resume the data flow by setting the pipeline back to the PLAYING state.
|
|
</para>
|
|
<note>
|
|
<para>
|
|
The PAUSED state is build for temporarily freezing the pipeline. Elements will typically
|
|
do not free their resources in the PAUSED state. Use the NULL state if you want to stop
|
|
the data flow permanantly.
|
|
</para>
|
|
</note>
|
|
<para>
|
|
The pipeline has to be in the PAUSED or NULL state if you want to insert or modify an element
|
|
in the pipeline. We will cover dynamic pipeline behaviour in ... <!-- fixme -->
|
|
</para>
|
|
</sect1>
|
|
|
|
</chapter>
|