mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-15 22:01:27 +00:00
816 lines
28 KiB
XML
816 lines
28 KiB
XML
<?xml version='1.0'?>
|
|
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [
|
|
<!ENTITY % magic-entities SYSTEM "magic">
|
|
%magic-entities;
|
|
|
|
<!ENTITY TITLEPAGE SYSTEM "titlepage.xml">
|
|
<!ENTITY INTRO SYSTEM "intro.xml">
|
|
<!ENTITY TESTAPP SYSTEM "testapp.xml">
|
|
<!ENTITY LOOPBASED SYSTEM "loopbased.xml">
|
|
<!ENTITY BUFFERS SYSTEM "buffers.xml">
|
|
<!ENTITY SRCNSINK SYSTEM "srcnsink.xml">
|
|
<!ENTITY STATEMANAGE SYSTEM "statemanage.xml">
|
|
<!ENTITY CHECKLIST SYSTEM "checklist.xml">
|
|
<!ENTITY GStreamer "<application>GStreamer</application>">
|
|
]>
|
|
|
|
<book id="index">
|
|
&TITLEPAGE;
|
|
|
|
<!-- ############# part ############### -->
|
|
|
|
<part id="introduction"><title>Introduction</title>
|
|
<partintro>
|
|
<para>
|
|
&GStreamer; is a framework for creating
|
|
streaming media applications. It is extremely powerful and versatile,
|
|
and this versatility stems in part from its modularity, and its ability
|
|
to incorporate new modules seamlessly into its framework.
|
|
This document describes how to extend the capabilities of
|
|
&GStreamer; by creating new plugins.
|
|
</para>
|
|
<para>
|
|
It first describes the concepts required and the ways in which
|
|
&GStreamer; can be extended. It then goes
|
|
through a worked example of how to write a simple filter (for data
|
|
processing), and how to test and debug it. More advanced concepts are
|
|
then introduced, with worked examples of each. Next, writing source
|
|
and sink elements (for performing input and output) is discussed.
|
|
Finally, checklists of things to be sure to do when extending
|
|
&GStreamer; are presented.
|
|
</para>
|
|
</partintro>
|
|
|
|
&INTRO;
|
|
</part>
|
|
|
|
<!-- ############ part ############# -->
|
|
|
|
<part id="basic-concepts"><title>Basic concepts</title>
|
|
<partintro>
|
|
<para>
|
|
|
|
This section introduces the basic concepts required to understand the
|
|
issues involved in extending &GStreamer;
|
|
</para>
|
|
<para>
|
|
Many of these concepts are explained in greater detail in the
|
|
GStreamer Application Development Manual, and are merely mentioned
|
|
here to refresh your memory.
|
|
|
|
</para>
|
|
</partintro>
|
|
|
|
|
|
<chapter id="cha-plugins">
|
|
<title>Plugins</title>
|
|
<para>
|
|
Extensions to &GStreamer; can be made using a plugin mechanism. This is
|
|
used extensively in &GStreamer; even if only the standard package is
|
|
being used: a few very basic functions reside in the core library, and
|
|
all others are implemented in plugins.
|
|
</para>
|
|
<para>
|
|
Plugins are only loaded when needed: a plugin registry is used to
|
|
store the details of the plugins so that it is not neccessary to load
|
|
all plugins to determine which are needed.
|
|
This registry needs to be updated whenever a new plugin is added to the
|
|
system: see the <emphasis>gstreamer-register</emphasis> utility and the
|
|
documentation in the <emphasis>GStreamer Application Development
|
|
Manual</emphasis> for more details.
|
|
</para>
|
|
<para>
|
|
User extensions to &GStreamer; can be installed in the main plugin
|
|
directory, and will immediately be available for use in applications.
|
|
<emphasis>gstreamer-register</emphasis> should be run to update
|
|
the repository: but the system should work correctly even if it hasn't
|
|
been - it will just take longer to load the correct plugin.
|
|
</para>
|
|
<para>
|
|
User specific plugin directories and registries will be available
|
|
in future versions of &GStreamer;.
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-elements">
|
|
<title>Elements</title>
|
|
<para>
|
|
Elements are at the core of &GStreamer;. Without elements, &GStreamer;
|
|
is just
|
|
a bunch of pipe fittings with nothing to connect. A large number of
|
|
elements (filters, sources and sinks) ship with &GStreamer;, but extra
|
|
elements can also be written.
|
|
</para>
|
|
<para>
|
|
An element may be constructed in several different ways, but all must
|
|
conform to the same basic rules. A simple filter may be built with the
|
|
FilterFactory, where the only code that need be written is the actual
|
|
filter code. A more complex filter, or a source or sink, will need to
|
|
be written out fully for complete access to the features and
|
|
performance possible with &GStreamer;.
|
|
</para>
|
|
<para>
|
|
The implementation of a new element will be contained in a plugin:
|
|
a single plugin may contain the implementation of several elements, or
|
|
just a single one.
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-buffers">
|
|
<title>Buffers</title>
|
|
<para>
|
|
Buffers are structures used to pass data between elements. All streams
|
|
of data are chopped up into chunks which are stored in buffers.
|
|
Buffers can be of any size, and also contain metadata indicating the
|
|
type of data contained in them. Buffers can be allocated by various
|
|
different schemes, and may either be passed on by elements or
|
|
unreferenced (and the memory used by the buffer freed).
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-typing">
|
|
<title>Typing and Properties</title>
|
|
<para>
|
|
A type system is used to ensure that the data passed between elements
|
|
is in a recognised format, and that the various parameters required
|
|
to fully specify that format match up correctly. Each connection
|
|
that is made between elements has a specified type. This is related,
|
|
but different, to the metadata in buffers which describes the type
|
|
of data in that particular buffer. See later in this document for
|
|
details of the available types.
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-metadata">
|
|
<title>Metadata</title>
|
|
<para>
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-scheduling">
|
|
<title>Scheduling</title>
|
|
<para>
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-chainloop">
|
|
<title>Chain vs Loop Elements</title>
|
|
<para>
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-autopluggers">
|
|
<title>Autopluggers</title>
|
|
<para>
|
|
&GStreamer; has an autoplugging mechanism, which enables application
|
|
writers to simply specify start and end elements for a path, and
|
|
the system will then create a path which links these elements,
|
|
in accordance with the type information provided by the elements.
|
|
</para>
|
|
<para>
|
|
It is possible to devise many different schemes for generating such
|
|
pathways, perhaps to optimise based on special criteria, or with
|
|
some specific constraints. It is thus possible to define new
|
|
autoplugging systems, using the plugin system.
|
|
</para>
|
|
</chapter>
|
|
|
|
</part>
|
|
|
|
<!-- ############ part ############# -->
|
|
|
|
<part id="typesnprops"><title>Types and Properties</title>
|
|
<partintro>
|
|
<para>
|
|
There is a very large set of possible types that may be used to
|
|
pass data between elements. Indeed, each new element that is defined
|
|
may use a new data format (though unless at least one other element
|
|
recognises that format, it will be most likely be useless since
|
|
nothing will be able to link with it).
|
|
</para>
|
|
<para>
|
|
In order for types to be useful, and for systems like autopluggers to
|
|
work, it is neccessary that all elements
|
|
agree on the type definitions, and which properties are required
|
|
for each type. The &GStreamer; framework itself
|
|
simply provides the ability to define types and parameters, but does
|
|
not fix the meaning of types and parameters, and does not enforce
|
|
standards on the creation of new types. This is a matter for
|
|
a policy to decide, not technical systems to enforce.
|
|
</para>
|
|
<para>
|
|
For now, the policy is simple:
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
Do not create a new type if you could use one which already
|
|
exists.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
If creating a new type, discuss it first with the other
|
|
&GStreamer; developers, on at least one of: IRC, mailing lists,
|
|
the &GStreamer; wiki.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Try to ensure that the name for a new format is as unlikely to
|
|
conflict with anything else created already, and is not a more
|
|
generalised name than it should be. For example:
|
|
"audio/compressed" would be too generalised a name to represent
|
|
audio data compressed with an mp3 codec. Instead "audio/mp3"
|
|
might be an appropriate name, or "audio/compressed" could exist
|
|
and have a property indicating the type of compression used.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Ensure that, when you do create a new type, you specify it
|
|
clearly, and get it added to the list of known types so that
|
|
other developers can use the type correctly when writing their
|
|
elements.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</partintro>
|
|
|
|
<chapter id="cha-basic-types">
|
|
<title>The basic types</title>
|
|
<para>
|
|
This is a list of the basic types used for buffers. For each type, we
|
|
give the name ("mime type") of the type, the list of properties which
|
|
are associated with the type, the meaning of each property, and the
|
|
purpose of the type.
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
<emphasis>audio/raw</emphasis>
|
|
- Unstructured and uncompressed raw audio data.
|
|
</para><para>
|
|
<emphasis>rate</emphasis>
|
|
- The sample rate of the data, in samples per second.
|
|
</para><para>
|
|
<emphasis>channels</emphasis>
|
|
- The number of channels of audio data.
|
|
</para><para>
|
|
<emphasis>format</emphasis>
|
|
- This describes the format in which the audio data is passed.
|
|
This is a string for which there are currently two valid values:
|
|
"int" for integer data and "float" for floating point data.
|
|
</para><para>
|
|
<emphasis>law</emphasis>
|
|
- Valid only if format=int. The law used to describe the data.
|
|
This is an integer for which there are three valid values: 0 for
|
|
linear, 1 for mu law, 2 for A law.
|
|
</para><para>
|
|
<emphasis>endianness</emphasis>
|
|
- Valid only if format=int. The order of bytes in a sample. This
|
|
is a boolean: 0 means little-endian (ie, bytes are least
|
|
significant first), 1 means big-endian (ie, most significant byte
|
|
first).
|
|
</para><para>
|
|
<emphasis>signed</emphasis>
|
|
- Valid only if format=int. Whether the samples are signed or not.
|
|
This is a boolean: 0 means unsigned, 1 means signed.
|
|
</para><para>
|
|
<emphasis>width</emphasis>
|
|
- Valid only if format=int. The number of bits per sample. This
|
|
is extremely likely to be a multiple of 8, but as ever this is up
|
|
to each element supporting this format to specify.
|
|
</para><para>
|
|
<emphasis>depth</emphasis>
|
|
- Valid only if format=int. The number of bits used per sample.
|
|
This must be less than or equal to the width: if less than the
|
|
width, the low bits are assumed to be the ones used. For example,
|
|
width=32, depth=24 means that each sample is stored in a 32 bit
|
|
word, but only the low 24 bits are actually used.
|
|
</para><para>
|
|
<emphasis>layout</emphasis>
|
|
- Valid only if format=float. A string representing the way in
|
|
which the floating point data is represented. For now, the only
|
|
valid value is gfloat, meaning that the data is passed as a series
|
|
of gfloat values.
|
|
</para><para>
|
|
<emphasis>intercept</emphasis>
|
|
- Valid only if format=float. A floating point value representing
|
|
the value that the signal "centres" on.
|
|
</para><para>
|
|
<emphasis>slope</emphasis>
|
|
- Valid only if format=float. A floating point value representing
|
|
how far the signal deviates from the intercept. So a slope of 1.0
|
|
and an intercept of 0.0 would mean an audio signal with minimum
|
|
and maximum values of -1.0 and 1.0. A slope of 0.5 and intercept
|
|
of 0.5 would represent values in the range 0.0 to 1.0.
|
|
</para>
|
|
<para>
|
|
For example: 16 bit integer, unsigned, linear, monophonic, big-endian,
|
|
44100KHz audio would be represented by
|
|
"format=int,law=0,endianness=1,signed=0,width=16,depth=16,rate=44100,channels=1"
|
|
and floating point, using gfloat's, in the range -1.0 to 1.0,
|
|
8000KHz stereo audio would be represented by
|
|
"format=float,layout=gfloat,intercept=0.0,slope=1.0,rate=8000,channels=2"
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
<emphasis>audio/mp3</emphasis>
|
|
- Audio data compressed using the mp3 encoding scheme.
|
|
</para><para>
|
|
<emphasis>framed</emphasis>
|
|
- This is a boolean. If true (1), each buffer contains exactly
|
|
one frame. If false (0), frames and buffers do not (necessarily)
|
|
match up. If the data is not framed, the values of some of the
|
|
properties will not be available, but others will be assumed to
|
|
be constant throughout the file, or may be found in other ways.
|
|
</para><para>
|
|
<emphasis>layer</emphasis>
|
|
- The compression scheme layer used to compress the data.
|
|
This is an integer, and can currently have the value 1, 2
|
|
or 3.
|
|
</para><para>
|
|
<emphasis>bitrate</emphasis>
|
|
- The bitrate, in kilobits per second.
|
|
For VBR (variable bitrate) mp3 data, this is the average bitrate.
|
|
</para><para>
|
|
<emphasis>channels</emphasis>
|
|
- The number of channels of audio data present. This could
|
|
theoretically be any integer greater than 0, but in practice will
|
|
be either 1 or 2.
|
|
</para><para>
|
|
<emphasis>joint-stereo</emphasis>
|
|
- Boolean. If true, channels must not be zero. If true, this
|
|
implies that stereo data is stored as a combined signal and
|
|
the difference between the signals, rather than as two entirely
|
|
separate signals.
|
|
</para><para>
|
|
There are many other properties relevant for
|
|
<emphasis>audio/mp3</emphasis> data: these may be added to this
|
|
specification at a later date.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
<emphasis>audio/x-ogg</emphasis>
|
|
- Audio data compressed using the Ogg Vorbis encoding scheme.
|
|
There are currently no parameters defined for this type. FIXME.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
<emphasis>video/raw</emphasis>
|
|
- Raw video data.
|
|
</para><para>
|
|
<emphasis>fourcc</emphasis>
|
|
- A FOURCC code identifying the format in which this data is
|
|
stored. FOURCC (Four Character Code) is a simple system to
|
|
allow unambiguous identification of a video datastream format.
|
|
See <ulink
|
|
url="http://www.webartz.com/fourcc/"
|
|
type="http">http://www.webartz.com/fourcc/</ulink>
|
|
</para><para>
|
|
<emphasis>width</emphasis>
|
|
- The number of pixels wide that each video frame is.
|
|
</para><para>
|
|
<emphasis>height</emphasis>
|
|
- The number of pixels high that each video frame is.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
<emphasis>video/mpeg</emphasis>
|
|
- Video data compressed using an mpeg encoding scheme.
|
|
</para><para>
|
|
<emphasis>mpegversion</emphasis>
|
|
</para><para>
|
|
<emphasis>systemstream</emphasis>
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
<emphasis>video/avi</emphasis>
|
|
- Video data compressed using the AVI encoding scheme.
|
|
There are currently no parameters defined for this type. FIXME.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</chapter>
|
|
|
|
<chapter id="cha-types-test">
|
|
<title>Building a simple format for testing</title>
|
|
<para>
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-types-simplemime">
|
|
<title>A simple MIME type</title>
|
|
<para>
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-types-props">
|
|
<title>Type properties</title>
|
|
<para>
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-types-typefind">
|
|
<title>Typefind functions and autoplugging</title>
|
|
<para>
|
|
</para>
|
|
</chapter>
|
|
|
|
</part>
|
|
|
|
<!-- ############ part ############# -->
|
|
|
|
<part id="first-plugin"><title>Building our first plugin</title>
|
|
<partintro>
|
|
<para>
|
|
We are now have the neccessary concepts to build our first plugin.
|
|
We are going to build an element which has a single input pad and
|
|
a single output pad, and simply passes anything it reads on
|
|
the input pad through and out on the output pad. We will also
|
|
see where we could add code to convert this plugin into something
|
|
more useful.
|
|
</para>
|
|
<para>
|
|
The example code used in this section can be found in
|
|
<filename>examples/plugins/</filename>
|
|
</para>
|
|
</partintro>
|
|
|
|
<chapter id="cha-boilerplate">
|
|
<title>Constructing the boilerplate</title>
|
|
<para>
|
|
The first thing to do when making a new element is to specify some basic
|
|
details about it: what its name is, who wrote it, what version number it
|
|
is, etc. We also need to define an object to represent the element and to
|
|
store the data the element needs. I shall refer to these details
|
|
collectively as the <emphasis>boilerplate</emphasis>.
|
|
</para>
|
|
|
|
<sect1 id="sect-boilerplate-gobject">
|
|
<title>Doing it the hard way with GstObject</title>
|
|
<para>
|
|
The standard way of defining the boilerplate is simply to write some
|
|
code, and fill in some structures. The easiest way to do this is to
|
|
copy an example and modify according to your needs.
|
|
</para>
|
|
<para>
|
|
First we will examine the code you would be likely to place in a header
|
|
file (although since the interface to the code is entirely defined
|
|
by the pluging system, and doesn't depend on reading a header file,
|
|
this is not crucial.)
|
|
|
|
The code here can be found in
|
|
<filename>examples/plugins/example.h</filename>
|
|
</para>
|
|
|
|
<programlisting>
|
|
/* Definition of structure storing data for this element. */
|
|
typedef struct _GstExample GstExample;
|
|
|
|
struct _GstExample {
|
|
GstElement element;
|
|
|
|
GstPad *sinkpad,*srcpad;
|
|
|
|
gint8 active;
|
|
};
|
|
|
|
/* Standard definition defining a class for this element. */
|
|
typedef struct _GstExampleClass GstExampleClass;
|
|
struct _GstExampleClass {
|
|
GstElementClass parent_class;
|
|
};
|
|
|
|
/* Standard macros for defining types for this element. */
|
|
#define GST_TYPE_EXAMPLE \
|
|
(gst_example_get_type())
|
|
#define GST_EXAMPLE(obj) \
|
|
(GTK_CHECK_CAST((obj),GST_TYPE_EXAMPLE,GstExample))
|
|
#define GST_EXAMPLE_CLASS(klass) \
|
|
(GTK_CHECK_CLASS_CAST((klass),GST_TYPE_EXAMPLE,GstExample))
|
|
#define GST_IS_EXAMPLE(obj) \
|
|
(GTK_CHECK_TYPE((obj),GST_TYPE_EXAMPLE))
|
|
#define GST_IS_EXAMPLE_CLASS(obj) \
|
|
(GTK_CHECK_CLASS_TYPE((klass),GST_TYPE_EXAMPLE))
|
|
|
|
/* Standard function returning type information. */
|
|
GtkType gst_example_get_type(void);
|
|
</programlisting>
|
|
|
|
</sect1>
|
|
|
|
<sect1 id="sect-boilerplate-filterfactory">
|
|
<title>Doing it the easy way with FilterFactory</title>
|
|
<para>
|
|
A plan for the future is to create a FilterFactory, to make the
|
|
process of making a new filter a simple process of specifying a few
|
|
details, and writing a small amount of code to perform the actual
|
|
data processing.
|
|
</para>
|
|
<para>
|
|
Unfortunately, this hasn't yet been implemented. It is also likely
|
|
that when it is, it will not be possible to cover all the possibilities
|
|
available by writing the boilerplate yourself, so some plugins will
|
|
always need to be manually registered.
|
|
</para>
|
|
<para>
|
|
As a rough outline of what is planned: the FilterFactory will take a
|
|
list of appropriate function pointers, and data structures to define
|
|
a filter. With a reasonable measure of preprocessor magic, the
|
|
plugin writer will then simply need to provide definitions of the
|
|
functions and data structures desired, and a name for the filter, and
|
|
then call a macro from within plugin_init() which will register the
|
|
new filter. All the fluff that goes into the definition of a filter
|
|
will thus be hidden from view.
|
|
</para>
|
|
<para>
|
|
Ideally, we will come up with a way for various FilterFactory-provided
|
|
functions to be overridden, to the point where you can construct
|
|
almost the most complex stuff with it, it just saves typing.
|
|
</para>
|
|
<para>
|
|
Of course, the filter factory can be used to create sources and sinks
|
|
too: simply create a filter with only source or sink pads.
|
|
</para>
|
|
<para>
|
|
You may be thinking that this should really be called an
|
|
ElementFactory. Well, we agree, but there is already something else
|
|
justifiably ealled an ElementFactory (this is the thing which actually
|
|
makes instances of elements). There is also already something called
|
|
a PluginFactory. We just have too many factories and not enough words.
|
|
And since this isn't yet written, it doesn't get priority for claiming
|
|
a name.
|
|
</para>
|
|
</sect1>
|
|
</chapter>
|
|
|
|
<chapter id="cha-defineelt">
|
|
<title>Defining an element</title>
|
|
<para>
|
|
A new element is defined by creating an element factory. This is a
|
|
structure containing all the information needed to create an instance
|
|
of the element. Creating a factory requires two things: a type for
|
|
the element to be created
|
|
(this was defined in the boilerplate above: FIXME - reorganise),
|
|
and a GstElementDetails structure, which contains some
|
|
general information about the element to be created.
|
|
</para>
|
|
|
|
<sect1 id="sect-defineelt-eltdetails">
|
|
<title>GstElementDetails</title>
|
|
<para>
|
|
The GstElementDetails structure gives a heirarchical type for
|
|
the element, a human-readable description of the element, as
|
|
well as author and version data. The entries are:
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
A long, english, name for the element.
|
|
</para></listitem><listitem><para>
|
|
The type of the element, as a heirarchy. The heirarchy is defined
|
|
by specifying the top level category, followed by a "/", followed
|
|
by the next level category, etc. The type should be defined
|
|
according to the guidelines elsewhere in this document.
|
|
(FIXME: write the guidelines, and give a better reference to them)
|
|
</para></listitem><listitem><para>
|
|
A brief description of the purpose of the element.
|
|
</para></listitem><listitem><para>
|
|
The version number of the element. For elements in the main
|
|
GStreamer source code, this will often simply be VERSION, which is
|
|
a macro defined to be the version number of the current GStreamer
|
|
version. The only requirement, however, is that the version
|
|
number should increase monotonically.
|
|
</para><para>
|
|
Version numbers should be stored in major.minor.patch form: ie, 3
|
|
(decimal) numbers, separated by ".".
|
|
</para></listitem><listitem><para>
|
|
The name of the author of the element, optionally followed by
|
|
a contact email address in angle brackets.
|
|
</para></listitem><listitem><para>
|
|
The copyright details for the element.
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
<para>
|
|
For example:
|
|
</para>
|
|
<programlisting>
|
|
static GstElementDetails example_details = {
|
|
"An example plugin",
|
|
"Example/FirstExample",
|
|
"Shows the basic structure of a plugin",
|
|
VERSION,
|
|
"your name <your.name@your.isp>",
|
|
"(C) 2001",
|
|
};
|
|
</programlisting>
|
|
</sect1>
|
|
|
|
<sect1 id="sect-defineelt-constructors">
|
|
<title>Constructor functions</title>
|
|
<para>
|
|
Each element has two functions which are used for construction of
|
|
an element. These are the _class_init() function, which is used to
|
|
initialise the class (specifying what signals and arguments the class
|
|
has and setting up global state), and the _init() function, which
|
|
is used to initialise a specific instance of the class.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sect-defineelt-pads">
|
|
<title>Specifying the pads</title>
|
|
<para>
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sect-defineelt-fns">
|
|
<title>Attaching functions</title>
|
|
<para>
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sect-defineelt-chainfn">
|
|
<title>The chain function</title>
|
|
<para>
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sect-defineelt-arguments">
|
|
<title>Adding arguments</title>
|
|
<para>
|
|
Define arguments in enum.
|
|
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sect-defineelt-signals">
|
|
<title>Signals</title>
|
|
<para>
|
|
Define signals in enum.
|
|
|
|
</para>
|
|
</sect1>
|
|
</chapter>
|
|
|
|
<chapter id="cha-definetype">
|
|
<title>Defining a type</title>
|
|
<para>
|
|
A new type is defined by creating an type factory. This is a
|
|
structure containing all the information needed to create an instance
|
|
of the type.
|
|
</para>
|
|
</chapter>
|
|
|
|
<chapter id="cha-plugininit">
|
|
<title>The plugin_init function</title>
|
|
<para>
|
|
Once we have written code defining all the parts of the plugin,
|
|
we need to write the plugin_init() function. This is a special
|
|
function, which is called as soon as the plugin is loaded, and
|
|
must return a pointer to a newly allocated GstPlugin structure.
|
|
This structure contains the details of all the facilities provided
|
|
by the plugin, and is the mechanism by which the definitions are
|
|
made available to the rest of the &GStreamer; system. Helper
|
|
functions are provided to help fill the
|
|
structure: for future compatability it is recommended that these
|
|
functions are used, as documented below, rather than attempting to
|
|
access the structure directly.
|
|
</para>
|
|
<para>
|
|
Note that the information returned by the plugin_init() function
|
|
will be cached in a central registry. For this reason, it is
|
|
important that the same information is always returned by
|
|
the function: for example, it must not make element factories
|
|
available based on runtime conditions. If an element can only
|
|
work in certain conditions (for example, if the soundcard is not
|
|
being used by some other process) this must be reflected by the
|
|
element being unable to enter the READY state if unavailable, rather
|
|
than the plugin attempting to deny existence of the plugin.
|
|
</para>
|
|
|
|
<sect1 id="sect-plugininit-types">
|
|
<title>Registering new types</title>
|
|
<para>
|
|
|
|
</para>
|
|
<programlisting>
|
|
void gst_plugin_add_type(GstPlugin *plugin,
|
|
GstTypeFactory *factory);
|
|
</programlisting>
|
|
<para>
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sect-plugininit-filter">
|
|
<title>Registering new element factories</title>
|
|
<para>
|
|
</para>
|
|
<programlisting>
|
|
void gst_plugin_add_factory(GstPlugin *plugin,
|
|
GstElementFactory *factory);
|
|
</programlisting>
|
|
<para>
|
|
Multiple element factories can be provided by a single plugin:
|
|
all it needs to do is call gst_plugin_add_factory() for each
|
|
element factory it wishes to provide.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1 id="sect-plugininit-autopluggers">
|
|
<title>Registering new autopluggers</title>
|
|
<para>
|
|
</para>
|
|
<programlisting>
|
|
void gst_plugin_add_autoplugger(GstPlugin *plugin,
|
|
GstAutoplugFactory *factory);
|
|
</programlisting>
|
|
</sect1>
|
|
|
|
</chapter>
|
|
|
|
</part>
|
|
|
|
<!-- ############ part ############# -->
|
|
|
|
<part id="test-app"><title>Building a simple test application</title>
|
|
<partintro>
|
|
<para>
|
|
</para>
|
|
</partintro>
|
|
|
|
&TESTAPP;
|
|
</part>
|
|
|
|
<!-- ############ part ############# -->
|
|
|
|
<part id="loopbased"><title>Loop-based Elements</title>
|
|
<partintro>
|
|
<para>
|
|
</para>
|
|
</partintro>
|
|
|
|
&LOOPBASED;
|
|
</part>
|
|
|
|
<!-- ############ part ############# -->
|
|
|
|
<part id="buffersnmeta"><title>Buffers and Metadata</title>
|
|
<partintro>
|
|
<para>
|
|
</para>
|
|
</partintro>
|
|
|
|
&BUFFERS;
|
|
</part>
|
|
|
|
<!-- ############ part ############# -->
|
|
|
|
<part id="srcnsink"><title>Sources and Sinks</title>
|
|
<partintro>
|
|
<para>
|
|
</para>
|
|
</partintro>
|
|
|
|
&SRCNSINK;
|
|
</part>
|
|
|
|
<!-- ############ part ############# -->
|
|
|
|
<part id="statemanage"><title>State management</title>
|
|
<partintro>
|
|
<para>
|
|
</para>
|
|
</partintro>
|
|
|
|
&STATEMANAGE;
|
|
</part>
|
|
|
|
<!-- ############ part ############# -->
|
|
|
|
<part id="checklist"><title>Checklist</title>
|
|
<partintro>
|
|
<para>
|
|
</para>
|
|
</partintro>
|
|
|
|
&CHECKLIST;
|
|
</part>
|
|
|
|
</book>
|