Chapter 27. Introduction to SMIL
SMIL (Synchronized
Multimedia Integration Language, pronounced "smile") is a
markup language (like HTML) for combining audio, video, text,
animation, and graphics in a precise, synchronized fashion. A SMIL
file instructs the client to retrieve media elements that reside on
the server as standalone files. Those separate elements are then
assembled and played by the SMIL player. The advantages of SMIL
include the ability to:
-
Integrate media elements in a time-based presentation
-
Reuse media elements in multiple presentations
-
Allow users to choose the media tracks they prefer, for example,
based on connection speed or language preferences
-
Add hyperlinks in a time-based presentation
SMIL is good for simple multimedia presentations, such as audio
slideshows and videos with scrolling captions. However, it is not a
substitute for the rich, high-impact interactivity offered by Flash
or Shockwave.
The SMIL 1.0 recommendation, released in June of 1998, is one of the
first XML-based DTDs proposed by the W3C (for an explanation of XML,
see Chapter 30, "Introduction to XML"). As of this writing, SMIL 2.0,
which greatly expands upon the functionality established in the
initial specification, is on the verge of becoming a formal
recommendation. The SMIL 2.0 specification is broken down into
function-specific modules which can potentially be used with other
XML languages. One proposed use, XHTML and SMIL, would allow
time-based behaviors to be added to HTML elements without the use of
a scripting language.
This chapter provides an introduction to how SMIL works and the
elements used to control the timing and display of multimedia
presentations.
27.1. How SMIL Works
SMIL uses tags to control the layout and timeline of a multimedia
presentation. It is fairly intuitive, so the best way to get a quick
understanding of SMIL is to look at a simple example. The following
SMIL code creates a 15-second-long narrated slideshow, in which an
audio track plays as a series of three images display in sequence.
<par dur="15s">
<audio src="audio_file.mp3" begin="0s">
<seq>
<img src="image_1.jpg" begin="0s">
<img src="image_2.jpg" begin="5s">
<img src="image_3.jpg" begin="10s">
</seq>
</par>
Looking at the code, it is easy to pick out the audio and image
elements. Each points to a separate media file on the server.
All elements contained within the <par>
element are played in parallel (at the same time); therefore, the
audio will continue playing as the images are displayed. The image
elements are contained in the <seq> element,
which means they will be played one after another (in sequence). The
begin attribute gives timing instructions for when
each element should be displayed. In our example, the images will
display in slideshow fashion every five seconds.
 |  |  | | 26.9. Director Online Resources |  | 27.2. SMIL Players |
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