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