2 <!-- ############ chapter ############# -->
4 <chapter id="chapter-intro-preface" xreflabel="Preface">
7 <!-- ############ sect1 ############# -->
9 <sect1 id="section-intro-what"><!-- synchronize with AppDevMan -->
10 <title>What is &GStreamer;?</title>
12 &GStreamer; is a framework for creating streaming media applications.
13 The fundamental design comes from the video pipeline at Oregon Graduate
14 Institute, as well as some ideas from DirectShow.
18 &GStreamer;'s development framework makes it possible to write any
19 type of streaming multimedia application. The &GStreamer; framework
20 is designed to make it easy to write applications that handle audio
21 or video or both. It isn't restricted to audio and video, and can
22 process any kind of data flow.
23 The pipeline design is made to have little overhead above what the
24 applied filters induce. This makes &GStreamer; a good framework for
25 designing even high-end audio applications which put high demands on
26 latency or performance.
30 One of the most obvious uses of &GStreamer; is using it to build
31 a media player. &GStreamer; already includes components for building a
32 media player that can support a very wide variety of formats, including
33 MP3, Ogg/Vorbis, MPEG-1/2, AVI, Quicktime, mod, and more. &GStreamer;,
34 however, is much more than just another media player. Its main advantages
35 are that the pluggable components can be mixed and matched into arbitrary
36 pipelines so that it's possible to write a full-fledged video or audio
41 The framework is based on plugins that will provide the various codec
42 and other functionality. The plugins can be linked and arranged in
43 a pipeline. This pipeline defines the flow of the data.
47 The &GStreamer; core function is to provide a framework for plugins,
48 data flow, synchronization and media type handling/negotiation. It
49 also provides an API to write applications using the various plugins.
53 <!-- ############ sect1 ############# -->
55 <sect1 id="section-preface-who" xreflabel="Who Should Read This Guide?">
56 <title>Who Should Read This Guide?</title>
58 This guide explains how to write new modules for &GStreamer;. The guide is
59 relevant to several groups of people:
64 Anyone who wants to add support for new ways of processing data in
65 &GStreamer;. For example, a person in this group might want to create
66 a new data format converter, a new visualization tool, or a new
72 Anyone who wants to add support for new input and output devices. For
73 example, people in this group might want to add the ability to write
74 to a new video output system or read data from a digital camera or
80 Anyone who wants to extend &GStreamer; in any way. You need to have an
81 understanding of how the plugin system works before you can understand
82 the constraints that the plugin system places on the rest of the code.
83 Also, you might be surprised after reading this at how much can be
89 This guide is not relevant to you if you only want to use the existing
90 functionality of &GStreamer;, or if you just want to use an application
91 that uses &GStreamer;. If you are only interested in using existing
92 plugins to write a new application - and there are quite a lot of
93 plugins already - you might want to check the &GstAppDevMan;. If you
94 are just trying to get help with a &GStreamer; application, then you
95 should check with the user manual for that particular application.
99 <!-- ############ sect1 ############# -->
101 <sect1 id="section-preface-reading" xreflabel="Preliminary Reading">
102 <title>Preliminary Reading</title>
104 This guide assumes that you are somewhat familiar with the basic workings
105 of &GStreamer;. For a gentle introduction to programming concepts in
106 &GStreamer;, you may wish to read the &GstAppDevMan; first.
107 Also check out the other documentation available on the <ulink type="http"
108 url="http://gstreamer.freedesktop.org/documentation/">&GStreamer; web site</ulink>.
110 <para><!-- synchronize with AppDevMan -->
111 In order to understand this manual, you will need to have a basic
112 understanding of the C language.
113 Since &GStreamer; adheres to the GObject programming model, this guide
114 also assumes that you understand the basics of <ulink type="http"
115 url="http://developer.gnome.org/gobject/stable/pt01.html">GObject</ulink>
117 You may also want to have a look
118 at Eric Harlow's book <emphasis>Developing Linux Applications with
119 GTK+ and GDK</emphasis>.
123 <!-- ############ sect1 ############# -->
125 <sect1 id="section-preface-structure" xreflabel="Structure of This Guide">
126 <title>Structure of This Guide</title>
128 To help you navigate through this guide, it is divided into several large
129 parts. Each part addresses a particular broad topic concerning &GStreamer;
130 plugin development. The parts of this guide are laid out in the following
136 <xref linkend="part-building"/> -
137 Introduction to the structure of a plugin, using an example audio
138 filter for illustration.
141 This part covers all the basic steps you generally need to perform
142 to build a plugin, such as registering the element with &GStreamer;
143 and setting up the basics so it can receive data from and send data
144 to neighbour elements. The discussion begins by giving examples of
145 generating the basic structures and registering an element in
146 <xref linkend="chapter-building-boiler"/>. Then, you will learn how
147 to write the code to get a basic filter plugin working in <xref
148 linkend="chapter-building-pads"/>, <xref
149 linkend="chapter-building-chainfn"/> and <xref
150 linkend="chapter-statemanage-states"/>.
153 After that, we will show some of the GObject concepts on how to
154 make an element configurable for applications and how to do
155 application-element interaction in
156 <xref linkend="chapter-building-args"/> and <xref
157 linkend="chapter-building-signals"/>. Next, you will learn to build
158 a quick test application to test all that you've just learned in
159 <xref linkend="chapter-building-testapp"/>. We will just touch upon
160 basics here. For full-blown application development, you should
161 look at <ulink type="http"
162 url="http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/index.html">the
163 Application Development Manual</ulink>.
168 <xref linkend="part-advanced"/> -
169 Information on advanced features of &GStreamer; plugin development.
172 After learning about the basic steps, you should be able to create a
173 functional audio or video filter plugin with some nice features.
174 However, &GStreamer; offers more for plugin writers. This part of the
175 guide includes chapters on more advanced topics, such as scheduling,
176 media type definitions in &GStreamer;, clocks, interfaces and
177 tagging. Since these features are purpose-specific, you can read them
178 in any order, most of them don't require knowledge from other
182 The first chapter, named <xref linkend="chapter-scheduling"/>,
183 will explain some of the basics of element scheduling. It is not
184 very in-depth, but is mostly some sort of an introduction on why
185 other things work as they do. Read this chapter if you're interested
186 in &GStreamer; internals. Next, we will apply this knowledge and
187 discuss another type of data transmission than what you learned in
188 <xref linkend="chapter-building-chainfn"/>: <xref
189 linkend="chapter-scheduling"/>. Loop-based elements will give
190 you more control over input rate. This is useful when writing, for
191 example, muxers or demuxers.
194 Next, we will discuss media identification in &GStreamer; in <xref
195 linkend="chapter-building-types"/>. You will learn how to define
196 new media types and get to know a list of standard media types
197 defined in &GStreamer;.
200 In the next chapter, you will learn the concept of request- and
201 sometimes-pads, which are pads that are created dynamically, either
202 because the application asked for it (request) or because the media
203 stream requires it (sometimes). This will be in <xref
204 linkend="chapter-advanced-request"/>.
207 The next chapter, <xref linkend="chapter-advanced-clock"/>, will
208 explain the concept of clocks in &GStreamer;. You need this
209 information when you want to know how elements should achieve
210 audio/video synchronization.
213 The next few chapters will discuss advanced ways of doing
214 application-element interaction. Previously, we learned on the
215 GObject-ways of doing this in <xref linkend="chapter-building-args"/>
216 and <xref linkend="chapter-building-signals"/>. We will discuss
217 dynamic parameters, which are a way of defining element behaviour
218 over time in advance, in <xref linkend="chapter-dparams"/>. Next,
219 you will learn about interfaces in <xref
220 linkend="chapter-advanced-interfaces"/>. Interfaces are very target-
221 specific ways of application-element interaction, based on GObject's
222 GInterface. Lastly, you will learn about how metadata is handled in
223 &GStreamer; in <xref linkend="chapter-advanced-tagging"/>.
226 The last chapter, <xref linkend="chapter-advanced-events"/>, will
227 discuss the concept of events in &GStreamer;. Events are, on the
228 one hand, another way of doing application-element interaction. It
229 takes care of seeking, for example. On the other hand, it is also
230 a way in which elements interact with each other, such as letting
231 each other know about media stream discontinuities, forwarding tags
232 inside a pipeline and so on.
237 <xref linkend="part-other"/> - Explanation
238 of writing other plugin types.
241 Because the first two parts of the guide use an audio filter as an
242 example, the concepts introduced apply to filter plugins. But many of
243 the concepts apply equally to other plugin types, including sources,
244 sinks, and autopluggers. This part of the guide presents the issues
245 that arise when working on these more specialized plugin types. The
246 chapter starts with a special focus on elements that can be written
247 using a base-class (<xref linkend="chapter-other-base"/>), and
248 later also goes into writing special types of elements in
249 <xref linkend="chapter-other-oneton"/>, <xref
250 linkend="chapter-other-ntoone"/> and <xref
251 linkend="chapter-other-manager"/>.
256 <xref linkend="part-appendix"/> - Further
257 information for plugin developers.
260 The appendices contain some information that stubbornly refuses
261 to fit cleanly in other sections of the guide. Most of this section
268 The remainder of this introductory part of the guide presents a short
269 overview of the basic concepts involved in &GStreamer; plugin development.
270 Topics covered include <xref linkend="section-basics-elements"/>, <xref
271 linkend="section-basics-pads"/>, <xref linkend="section-basics-data"/> and
272 <xref linkend="section-basics-types"/>. If you are already familiar with
273 this information, you can use this short overview to refresh your memory,
274 or you can skip to <xref linkend="part-building"/>.
277 As you can see, there a lot to learn, so let's get started!
283 Creating compound and complex elements by extending from a GstBin.
284 This will allow you to create plugins that have other plugins embedded
290 Adding new media types to the registry along with typedetect functions.
291 This will allow your plugin to operate on a completely new media type.