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Various updates to PWG; mainly adding information about types and properties.

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Original commit message from CVS:
Various updates to PWG; mainly adding information about types and
properties.
Removed concepts.sgml and typesnprops.sgml; merged into main file.  I was
finding that having all the separate subfiles simply stopped me from
finding what I wanted to edit.  Maybe I'll split it up again later, but
this is much better for now.
This commit is contained in:
Richard Boulton 2001-03-18 03:57:59 +00:00
parent 3534e68563
commit d5c2bc5f98
4 changed files with 240 additions and 118 deletions
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4
docs/fwg/Makefile.am
View file

@ -4,11 +4,9 @@ htmlname = index.html
sgml_files = gst-plugin-writers-guide.sgml \
titlepage.sgml \
intro.sgml \
concepts.sgml \
firstplugin.sgml \
testapp.sgml \
loopbased.sgml \
typesnprops.sgml
loopbased.sgml
fig_files =
eps_files =

85
docs/fwg/concepts.sgml
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@ -1,85 +0,0 @@
<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 in a standard set of plugins.
</para>
<para>
Plugins can extend GStreamer in several
</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 when 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>
</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-typing">
<title>Typing and Properties</title>
<para>
</para>
</chapter>
<chapter id="cha-metadata">
<title>Metadata</title>
<para>
</para>
</chapter>

245
docs/fwg/gst-plugin-writers-guide.sgml
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@ -3,16 +3,12 @@
<!ENTITY INTRO SYSTEM "intro.sgml">
<!ENTITY CONCEPTS SYSTEM "concepts.sgml">
<!ENTITY FIRSTPLUGIN SYSTEM "firstplugin.sgml">
<!ENTITY TESTAPP SYSTEM "testapp.sgml">
<!ENTITY LOOPBASED SYSTEM "loopbased.sgml">
<!ENTITY TYPESNPROPS SYSTEM "typesnprops.sgml">
<!ENTITY BUFFERS SYSTEM ".sgml">
<!ENTITY SRCNSINK SYSTEM ".sgml">
@ -62,11 +58,109 @@
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>
&CONCEPTS;
<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.
</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.
</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>
</part>
@ -119,10 +213,149 @@
<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>
&TYPESNPROPS;
<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>law</emphasis>
- 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>
- The order of bytes in a sample. This is an integer for
which there are two valid values: 0 for little-endian (ie, bytes
are least significant first), 1 for big-endian (ie, most
significant byte first).
</para><para>
<emphasis>signed</emphasis>
- Whether the samples are signed or not. This is an integer
for which there are two valid values: 0 for unsigned, 1 for
signed.
</para><para>
<emphasis>width</emphasis>
- 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>
- 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>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>
For example: 16 bit, unsigned, linear, monophonic, big-endian,
44100KHz audio would be represented by
"law=0,endianness=1,signed=0,width=16,depth=16,rate=44100,channels=1"
</para>
</listitem>
</itemizedlist>
<itemizedlist>
<listitem>
<para>
<emphasis>audio/mp3</emphasis>
</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 ############# -->

24
docs/fwg/typesnprops.sgml
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@ -1,24 +0,0 @@
<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>