topical media & game development
research directions -- architectural patterns
Facing the task of developing a multimedia information system,
there are many options.
Currently, the web seems to be the dominant infrastructure
upon which to build a multimedia system.
Now, assuming that we chose the web as our vehicle,
how should we approach building such a system or,
in other words,
what architectural patterns can we deploy to build
an actual multimedia information system?
As you undoubtly know,
the web is a document system that makes a clear distinction
between
servers that deliver documents
and
clients that display documents.
See
[OO], section
12.1.
At the
server-side you are free to do almost anything, as long as
the document is delivered in the proper format.
At the client-side, we have a generic document viewer
that is suitable for HTML with images and sound.
Dependent on the actual browser, a number of other
formats may be allowed.
However, in general, extensions with additional formats
are realized by so-called
plugins
that are loaded by the browser to enable a particular format,
such as
shockwave,
flash or
VRML.
Nowadays, there is an overwhelming number of formats including,
apart from the formats mentioned, audio and video formats
as well as a number of XML-based formats as for example SMIL and SVG.
For each of these formats the user (client) has to
download a plugin.
An
alternative to plugins (at the client-side) is provided
by Java
applets.
For Java applets the user does not need to download any
code, since the Java platform takes care of downloading
the necessary classes.
However, since applets may be of arbitrary complexity,
downloading the classes needed by an application may take
prohibitively long.
The actual situation at the client-side may be even more complex.
In many cases a media format does not only require
a plugin, but also an applet.
The plugin and applet can communicate with eachother through
a mechanism (introduced by Netscape under the name LiveConnect)
which allows for exchanging messages using the built-in DOM
(Document Object Model) of the browser.
In addition, the plugin and applet may be controlled
through Javascript (or VBscript).
A little dazzling at first perhaps,
but usually not to difficult to deal with in practice.
Despite the fact that the web provides a general infrasructure
for both (multimedia) servers and clients,
it might be worthwhile to explore other options,
at the client-side as well as the server-side.
In the following, we will look briefly at:
- the Java Media Framework, and
- the DLP+X3D platform
as examples of, respectively,
a framework for creating dedicated multimedia applications
at the client-side
and a framework for developing intelligent multimedia systems,
with client-side (rich media 3D) components as well as
additional server-side (agent) components.
Java Media Framework
The Java platform offers rich means to create (distributed) systems.
Also included are powerful GUI libraries (in particular, Swing),
3D libraries (Java3D) and libraries that allow
the use and manipulation of images, audio and video
(the Java Media Framework).
Or, in the words of the SUN web site:
java Media Framework
The JavaTM Media APIs meet the increasing demand for multimedia in the enterprise by providing a unified, non-proprietary, platform-neutral solution. This set of APIs supports the integration of audio and video clips, animated presentations, 2D fonts, graphics, and images, as well as speech input/output and 3D models. By providing standard players and integrating these supporting technologies, the Java Media APIs enable developers to produce and distribute compelling, media-rich content.
However, although Java was once
introduced as the dial tone of the Internet
(see [OO], section 6.3),
due to security restrictions on applets it is not always possible
to deploy media-rich applets, without taking recourse
to the Java plugin to circumvent these restrictions.
DLP+X3D
In our DLP+X3D platform, that is introduced
in section [7-3] and described in more detail
in appendix [platform],
we adopted a different approach by assuming the availability
of a generic X3D/VRML plugin with
a Java-based External Authoring Interface (EAI).
In addition, we deploy a high-level ditributed logic programming
language (DLP) to control the content and behavior
of the plugin.
Moreover, DLP may also be used for creating dedicated (intelligent)
servers to allow for multi-user applications.
The DLP language is Java-based and is loaded using an applet.
(The DLP jar file is of medium size, about 800 K,
and does not require the download of any additional code.)
Dua, again, to the security restrictions on applets,
additional DLP servers must reside on the site
from where the applet was downloaded.
Our plugin, which is currently the blaxxun VRML plugin, allows for incorporating a fairly
large number of rich media formats,
including (real) audio and (real) video.,
thus allowing for an integrated presentation environment
where rich media can be displayed in 3D space in a unified
manner.
A disadvantage of such a unified presentation format, however,
is that additional authoring effort is required
to realize the integration of the various formats.
(C) Æliens
04/09/2009
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