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296 lines
14 KiB
XML
296 lines
14 KiB
XML
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<!-- ############ chapter ############# -->
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<chapter id="chapter-intro-preface" xreflabel="Preface">
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<title>Preface</title>
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<!-- ############ sect1 ############# -->
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<sect1 id="section-intro-what"><!-- synchronize with AppDevMan -->
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<title>What is &GStreamer;?</title>
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<para>
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&GStreamer; is a framework for creating streaming media applications.
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The fundamental design comes from the video pipeline at Oregon Graduate
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Institute, as well as some ideas from DirectShow.
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</para>
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<para>
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&GStreamer;'s development framework makes it possible to write any
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type of streaming multimedia application. The &GStreamer; framework
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is designed to make it easy to write applications that handle audio
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or video or both. It isn't restricted to audio and video, and can
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process any kind of data flow.
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The pipeline design is made to have little overhead above what the
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applied filters induce. This makes &GStreamer; a good framework for
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designing even high-end audio applications which put high demands on
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latency or performance.
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</para>
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<para>
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One of the most obvious uses of &GStreamer; is using it to build
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a media player. &GStreamer; already includes components for building a
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media player that can support a very wide variety of formats, including
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MP3, Ogg/Vorbis, MPEG-1/2, AVI, Quicktime, mod, and more. &GStreamer;,
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however, is much more than just another media player. Its main advantages
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are that the pluggable components can be mixed and matched into arbitrary
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pipelines so that it's possible to write a full-fledged video or audio
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editing application.
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</para>
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<para>
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The framework is based on plugins that will provide the various codec
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and other functionality. The plugins can be linked and arranged in
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a pipeline. This pipeline defines the flow of the data.
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</para>
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<para>
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The &GStreamer; core function is to provide a framework for plugins,
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data flow, synchronization and media type handling/negotiation. It
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also provides an API to write applications using the various plugins.
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</para>
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</sect1>
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<!-- ############ sect1 ############# -->
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<sect1 id="section-preface-who" xreflabel="Who Should Read This Guide?">
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<title>Who Should Read This Guide?</title>
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<para>
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This guide explains how to write new modules for &GStreamer;. The guide is
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relevant to several groups of people:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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Anyone who wants to add support for new ways of processing data in
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&GStreamer;. For example, a person in this group might want to create
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a new data format converter, a new visualization tool, or a new
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decoder or encoder.
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</para>
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</listitem>
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<listitem>
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<para>
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Anyone who wants to add support for new input and output devices. For
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example, people in this group might want to add the ability to write
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to a new video output system or read data from a digital camera or
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special microphone.
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</para>
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</listitem>
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<listitem>
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<para>
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Anyone who wants to extend &GStreamer; in any way. You need to have an
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understanding of how the plugin system works before you can understand
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the constraints that the plugin system places on the rest of the code.
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Also, you might be surprised after reading this at how much can be
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done with plugins.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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This guide is not relevant to you if you only want to use the existing
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functionality of &GStreamer;, or if you just want to use an application
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that uses &GStreamer;. If you are only interested in using existing
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plugins to write a new application - and there are quite a lot of
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plugins already - you might want to check the &GstAppDevMan;. If you
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are just trying to get help with a &GStreamer; application, then you
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should check with the user manual for that particular application.
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</para>
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</sect1>
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<!-- ############ sect1 ############# -->
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<sect1 id="section-preface-reading" xreflabel="Preliminary Reading">
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<title>Preliminary Reading</title>
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<para>
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This guide assumes that you are somewhat familiar with the basic workings
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of &GStreamer;. For a gentle introduction to programming concepts in
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&GStreamer;, you may wish to read the &GstAppDevMan; first.
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Also check out the other documentation available on the <ulink type="http"
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url="http://gstreamer.freedesktop.org/documentation/">&GStreamer; web site</ulink>.
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</para>
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<para><!-- synchronize with AppDevMan -->
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In order to understand this manual, you will need to have a basic
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understanding of the C language.
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Since &GStreamer; adheres to the GObject programming model, this guide
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also assumes that you understand the basics of <ulink type="http"
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url="http://developer.gnome.org/gobject/stable/pt01.html">GObject</ulink>
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programming.
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You may also want to have a look
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at Eric Harlow's book <emphasis>Developing Linux Applications with
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GTK+ and GDK</emphasis>.
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</para>
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</sect1>
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<!-- ############ sect1 ############# -->
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<sect1 id="section-preface-structure" xreflabel="Structure of This Guide">
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<title>Structure of This Guide</title>
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<para>
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To help you navigate through this guide, it is divided into several large
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parts. Each part addresses a particular broad topic concerning &GStreamer;
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plugin development. The parts of this guide are laid out in the following
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order:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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<xref linkend="part-building"/> -
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Introduction to the structure of a plugin, using an example audio
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filter for illustration.
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</para>
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<para>
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This part covers all the basic steps you generally need to perform
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to build a plugin, such as registering the element with &GStreamer;
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and setting up the basics so it can receive data from and send data
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to neighbour elements. The discussion begins by giving examples of
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generating the basic structures and registering an element in
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<xref linkend="chapter-building-boiler"/>. Then, you will learn how
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to write the code to get a basic filter plugin working in <xref
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linkend="chapter-building-pads"/>, <xref
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linkend="chapter-building-chainfn"/> and <xref
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linkend="chapter-statemanage-states"/>.
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</para>
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<para>
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After that, we will show some of the GObject concepts on how to
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make an element configurable for applications and how to do
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application-element interaction in
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<xref linkend="chapter-building-args"/> and <xref
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linkend="chapter-building-signals"/>. Next, you will learn to build
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a quick test application to test all that you've just learned in
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<xref linkend="chapter-building-testapp"/>. We will just touch upon
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basics here. For full-blown application development, you should
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look at <ulink type="http"
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url="http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/index.html">the
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Application Development Manual</ulink>.
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</para>
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</listitem>
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<listitem>
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<para>
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<xref linkend="part-advanced"/> -
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Information on advanced features of &GStreamer; plugin development.
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</para>
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<para>
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After learning about the basic steps, you should be able to create a
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functional audio or video filter plugin with some nice features.
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However, &GStreamer; offers more for plugin writers. This part of the
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guide includes chapters on more advanced topics, such as scheduling,
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media type definitions in &GStreamer;, clocks, interfaces and
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tagging. Since these features are purpose-specific, you can read them
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in any order, most of them don't require knowledge from other
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sections.
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</para>
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<para>
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The first chapter, named <xref linkend="chapter-scheduling"/>,
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will explain some of the basics of element scheduling. It is not
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very in-depth, but is mostly some sort of an introduction on why
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other things work as they do. Read this chapter if you're interested
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in &GStreamer; internals. Next, we will apply this knowledge and
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discuss another type of data transmission than what you learned in
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<xref linkend="chapter-building-chainfn"/>: <xref
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linkend="chapter-scheduling"/>. Loop-based elements will give
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you more control over input rate. This is useful when writing, for
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example, muxers or demuxers.
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</para>
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<para>
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Next, we will discuss media identification in &GStreamer; in <xref
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linkend="chapter-building-types"/>. You will learn how to define
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new media types and get to know a list of standard media types
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defined in &GStreamer;.
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</para>
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<para>
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In the next chapter, you will learn the concept of request- and
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sometimes-pads, which are pads that are created dynamically, either
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because the application asked for it (request) or because the media
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stream requires it (sometimes). This will be in <xref
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linkend="chapter-advanced-request"/>.
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</para>
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<para>
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The next chapter, <xref linkend="chapter-advanced-clock"/>, will
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explain the concept of clocks in &GStreamer;. You need this
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information when you want to know how elements should achieve
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audio/video synchronization.
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</para>
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<para>
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The next few chapters will discuss advanced ways of doing
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application-element interaction. Previously, we learned on the
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GObject-ways of doing this in <xref linkend="chapter-building-args"/>
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and <xref linkend="chapter-building-signals"/>. We will discuss
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dynamic parameters, which are a way of defining element behaviour
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over time in advance, in <xref linkend="chapter-dparams"/>. Next,
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you will learn about interfaces in <xref
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linkend="chapter-advanced-interfaces"/>. Interfaces are very target-
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specific ways of application-element interaction, based on GObject's
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GInterface. Lastly, you will learn about how metadata is handled in
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&GStreamer; in <xref linkend="chapter-advanced-tagging"/>.
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</para>
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<para>
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The last chapter, <xref linkend="chapter-advanced-events"/>, will
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discuss the concept of events in &GStreamer;. Events are, on the
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one hand, another way of doing application-element interaction. It
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takes care of seeking, for example. On the other hand, it is also
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a way in which elements interact with each other, such as letting
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each other know about media stream discontinuities, forwarding tags
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inside a pipeline and so on.
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</para>
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</listitem>
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<listitem>
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<para>
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<xref linkend="part-other"/> - Explanation
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of writing other plugin types.
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</para>
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<para>
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Because the first two parts of the guide use an audio filter as an
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example, the concepts introduced apply to filter plugins. But many of
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the concepts apply equally to other plugin types, including sources,
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sinks, and autopluggers. This part of the guide presents the issues
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that arise when working on these more specialized plugin types. The
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chapter starts with a special focus on elements that can be written
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using a base-class (<xref linkend="chapter-other-base"/>), and
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later also goes into writing special types of elements in
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<xref linkend="chapter-other-oneton"/>, <xref
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linkend="chapter-other-ntoone"/> and <xref
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linkend="chapter-other-manager"/>.
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</para>
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</listitem>
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<listitem>
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<para>
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<xref linkend="part-appendix"/> - Further
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information for plugin developers.
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</para>
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<para>
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The appendices contain some information that stubbornly refuses
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to fit cleanly in other sections of the guide. Most of this section
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is not yet finished.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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The remainder of this introductory part of the guide presents a short
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overview of the basic concepts involved in &GStreamer; plugin development.
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Topics covered include <xref linkend="section-basics-elements"/>, <xref
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linkend="section-basics-pads"/>, <xref linkend="section-basics-data"/> and
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<xref linkend="section-basics-types"/>. If you are already familiar with
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this information, you can use this short overview to refresh your memory,
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or you can skip to <xref linkend="part-building"/>.
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</para>
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<para>
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As you can see, there a lot to learn, so let's get started!
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</para>
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<itemizedlist>
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<listitem>
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<para>
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Creating compound and complex elements by extending from a GstBin.
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This will allow you to create plugins that have other plugins embedded
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in them.
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</para>
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</listitem>
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<listitem>
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<para>
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Adding new media types to the registry along with typedetect functions.
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This will allow your plugin to operate on a completely new media type.
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</para>
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</listitem>
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</itemizedlist>
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</sect1>
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</chapter>
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