gstreamer/docs/manual/intro-motivation.xml
Ronald S. Bultje f24de41e35 docs/manual/intro-motivation.xml: Fix typos.
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Reviewed by:  Ronald S. Bultje  <rbultje@ronald.bitfreak.net>
* docs/manual/intro-motivation.xml:
Fix typos.
2004-12-16 10:53:47 +00:00

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<chapter id="chapter-motivation">
<title>Motivation &amp; Goals</title>
<para>
Linux has historically lagged behind other operating systems in the
multimedia arena. Microsoft's <trademark>Windows</trademark> and
Apple's <trademark>MacOS</trademark> both have strong support for
multimedia devices, multimedia content creation, playback, and
realtime processing. Linux, on the other hand, has a poorly integrated
collection of multimedia utilities and applications available, which
can hardly compete with the professional level of software available
for MS Windows and MacOS.
</para>
<para>
GStreamer was designed to provide a solution to the current Linux media
problems.
</para>
<sect1 id="section-motivation-problems">
<title>Current problems</title>
<para>
We describe the typical problems in today's media handling on Linux.
</para>
<sect2 id="section-motivation-duplicate">
<title>Multitude of duplicate code</title>
<para>
The Linux user who wishes to hear a sound file must hunt through
their collection of sound file players in order to play the tens
of sound file formats in wide use today. Most of these players
basically reimplement the same code over and over again.
</para>
<para>
The Linux developer who wishes to embed a video clip in their
application must use crude hacks to run an external video player.
There is no library available that a developer can use to create
a custom media player.
</para>
</sect2>
<sect2 id="section-motivation-goal">
<title>'One goal' media players/libraries</title>
<para>
Your typical MPEG player was designed to play MPEG video and audio.
Most of these players have implemented a complete infrastructure
focused on achieving their only goal: playback. No provisions were
made to add filters or special effects to the video or audio data.
</para>
<para>
If you want to convert an MPEG-2 video stream into an AVI file,
your best option would be to take all of the MPEG-2 decoding
algorithms out of the player and duplicate them into your own
AVI encoder. These algorithms cannot easily be shared across
applications.
</para>
<para>
Attempts have been made to create libraries for handling various
media types. Because they focus on a very specific media type
(avifile, libmpeg2, ...), significant work is needed to integrate
them due to a lack of a common API. &GStreamer; allows you to
wrap these libraries with a common API, which significantly
simplifies integration and reuse.
</para>
</sect2>
<sect2 id="section-motivation-plugin">
<title>Non unified plugin mechanisms</title>
<para>
Your typical media player might have a plugin for different media
types. Two media players will typically implement their own plugin
mechanism so that the codecs cannot be easily exchanged. The plugin
system of the typical media player is also very tailored to the
specific needs of the application.
</para>
<para>
The lack of a unified plugin mechanism also seriously hinders the
creation of binary only codecs. No company is willing to port their
code to all the different plugin mechanisms.
</para>
<para>
While &GStreamer; also uses it own plugin system it offers a very rich
framework for the plugin developer and ensures the plugin can be used
in a wide range of applications, transparently interacting with other
plugins. The framework that &GStreamer; provides for the plugins is
flexible enough to host even the most demanding plugins.
</para>
</sect2>
<sect2 id="section-motivation-experience">
<title>Poor user experience</title>
<para>
Because of the problems mentioned above, application authors have
so far often been urged to spend a considerable amount of time in
writing their own backends, plugin mechanisms and so on. The result
has often been, unfortunately, that both the backend as well as the
user interface were only half-finished. Demotivated, the application
authors would start rewriting the whole thing and complete the circle.
This leads to a <emphasis>poor end user experience</emphasis>.
</para>
</sect2>
<sect2 id="section-motivation-network">
<title>Provision for network transparency</title>
<para>
No infrastructure is present to allow network transparent media
handling. A distributed MPEG encoder will typically duplicate the
same encoder algorithms found in a non-distributed encoder.
</para>
<para>
No provisions have been made for technologies such as
the <ulink url="http://developer.gnome.org/arch/component/bonobo.html"
type="http">GNOME object embedding using Bonobo</ulink>.
</para>
<para>
The &GStreamer; core does not use network transparent technologies
at the lowest level as it only adds overhead for the local case.
That said, it shouldn't be hard to create a wrapper around the
core components. There are tcp plugins now that implement a
&GStreamer; Data Protocol that allows pipelines to be slit over
TCP. These are located in the gst-plugins module directory gst/tcp.
</para>
</sect2>
<sect2 id="section-motivation-catchup">
<title>Catch up with the <trademark>Windows</trademark> world</title>
<para>
We need solid media handling if we want to see Linux succeed on
the desktop.
</para>
<para>
We must clear the road for commercially backed codecs and multimedia
applications so that Linux can become an option for doing multimedia.
</para>
</sect2>
</sect1>
<sect1 id="section-goals-design">
<title>The design goals</title>
<para>
We describe what we try to achieve with &GStreamer;.
</para>
<sect2 id="section-goals-clean">
<title>Clean and powerful</title>
<para>
&GStreamer; wants to provide a clean interface to:
</para>
<itemizedlist>
<listitem>
<para>
The application programmer who wants to build a media pipeline.
The programmer can use an extensive set of powerful tools to create
media pipelines without writing a single line of code. Performing
complex media manipulations becomes very easy.
</para>
</listitem>
<listitem>
<para>
The plugin programmer. Plugin programmers are provided a clean and
simple API to create self-contained plugins. An extensive debugging
and tracing mechanism has been integrated. GStreamer also comes with
an extensive set of real-life plugins that serve as examples too.
</para>
</listitem>
</itemizedlist>
</sect2>
<sect2 id="section-goals-object">
<title>Object oriented</title>
<para>
&GStreamer; adheres to the GLib 2.0 object model. A programmer
familiar with GLib 2.0 or older versions of GTK+ will be
comfortable with &GStreamer;.
</para>
<para>
&GStreamer; uses the mechanism of signals and object properties.
</para>
<para>
All objects can be queried at runtime for their various properties and
capabilities.
</para>
<para>
&GStreamer; intends to be similar in programming methodology to GTK+.
This applies to the object model, ownership of objects, reference
counting, ...
</para>
</sect2>
<sect2 id="section-goals-extensible">
<title>Extensible</title>
<para>
All &GStreamer; Objects can be extended using the GObject
inheritance methods.
</para>
<para>
All plugins are loaded dynamically and can be extended and upgraded
independently.
</para>
</sect2>
<sect2 id="section-goals-binary">
<title>Allow binary only plugins</title>
<para>
Plugins are shared libraries that are loaded at runtime. Since all
the properties of the plugin can be set using the GObject properties,
there is no need (and in fact no way) to have any header files
installed for the plugins.
</para>
<para>
Special care has been taken to make plugins completely self-contained.
All relevant aspects of plugins can be queried at run-time.
</para>
</sect2>
<sect2 id="section-goals-performance">
<title>High performance</title>
<para>
High performance is obtained by:
</para>
<itemizedlist>
<listitem>
<para>
using GLib's <function>g_mem_chunk</function> and fast
non-blocking allocation algorithms where possible to
minimize dynamic memory allocation.
</para>
</listitem>
<listitem>
<para>
extremely light-weight links between plugins. Data can travel
the pipeline with minimal overhead. Data passing between
plugins only involves a pointer dereference in a typical
pipeline.
</para>
</listitem>
<listitem>
<para>
providing a mechanism to directly work on the target memory.
A plugin can for example directly write to the X server's
shared memory space. Buffers can also point to arbitrary
memory, such as a sound card's internal hardware buffer.
</para>
</listitem>
<listitem>
<para>
refcounting and copy on write minimize usage of memcpy.
Sub-buffers efficiently split buffers into manageable pieces.
</para>
</listitem>
<listitem>
<para>
the use of cothreads to minimize the threading overhead.
Cothreads are a simple and fast user-space method for
switching between subtasks. Cothreads were measured to
consume as little as 600 cpu cycles.
</para>
</listitem>
<listitem>
<para>
allowing hardware acceleration by using specialized plugins.
</para>
</listitem>
<listitem>
<para>
using a plugin registry with the specifications of the plugins so
that the plugin loading can be delayed until the plugin is actually
used.
</para>
</listitem>
<listitem>
<para>
all critical data passing is free of locks and mutexes.
</para>
</listitem>
</itemizedlist>
</sect2>
<sect2 id="section-goals-separation">
<title>Clean core/plugins separation</title>
<para>
The core of &GStreamer; is essentially media-agnostic. It only knows
about bytes and blocks, and only contains basic elements.
The core of &GStreamer; is functional enough to even implement
low-level system tools, like cp.
</para>
<para>
All of the media handling functionality is provided by plugins
external to the core. These tell the core how to handle specific
types of media.
</para>
</sect2>
<sect2 id="section-goals-testbed">
<title>Provide a framework for codec experimentation</title>
<para>
&GStreamer; also wants to be an easy framework where codec
developers can experiment with different algorithms, speeding up
the development of open and free multimedia codecs like <ulink
url="http://www.xiph.org/ogg/index.html" type="http">Theora and
Vorbis</ulink>.
</para>
</sect2>
</sect1>
</chapter>