Synchronized Multimedia Integration Language (SMIL) is widely used for
authoring multimedia presentations. To create a presentation in SMIL
consisting of other XML documents is not very handy, though. In
addition to images, audio and video, a presentation can contain
elements from other XML documents, like XHTML. To include a formatted
HTML text element into a SMIL document, an external HTML document must
be
added to the timeline and the actual formatting of the element is done
in the external document. A better idea would be to create one XML
document with the contents and handle the formatting and timing of the
document separately. For formatting, one can use e.g. Cascading Style
Sheets. For temporal structure, Timesheets language has
been proposed [1].
Timesheets
Timesheets can be seen as a temporal counterpart for Cascading Style
Sheets. Whereas CSS defines the spatial layout of the document and
formatting of the elements, Timesheets specify what elements are active
at a certain moment. And as with CSS, Timesheets can be reused in
multiple documents, which can provide a common temporal layout for
multimedia presentations with different contents but identical
storylines. The document can be shown in a user agent even if the
Timesheets are not supported, since the contents
and the layout are still governed by the document itself. Of course,
the temporal aspect of the document is then lost, since all the
elements are active all the time.
A simple example of the Timesheets is shown below. It shows a general
XHTML document that could be, for example a
single slide from a slideshow. When the document is viewed, first only
the title "Introduction" and the page number are shown. Then, after two
seconds, the text of the first bullet is shown, followed by the next
bullet every two seconds. The placement and styling of the elements are
specified in the CSS, the Timesheet only specify the visibility of the
elements at a given moment in time.
<p id="title">Introduction</p>
<p id="bullet1">o Some intro to WLAN</p>
<p id="bullet2">o Some intro to WLAN</p>
<p id="bullet3">- Subbullet</p>
<p id="bullet4">- Subbullet</p>
<p id="pagenum">2</p>
</div>
</body>
A
simple example of an XHTML document with Timesheets
A basic implementation of Timesheets is being developed at HUT under
the X-Smiles project (http://www.xsmiles.org).
X-Smiles is an XML browser, which supports several XML specifications
and general XML documents styled by CSS. In addition, temporal styling
of a document is supported through Timesheets.
The Timesheet implementation is based on the work by W. Kate et. al. [1]
and W3C Recommendation of SMIL 2.0. Currently, the
implementation supports the basic SMIL functionality, including
parallel and sequential time containers, events
and prefetching contents. A few demos has also been created as a proof
of concept.
References
[1] Kate, W. et. al., "Timesheets - Integrating
Timing in XML", WWW9 Workshop: Multimedia on Web, 2000.