Authoring a SMIL presentation comes down, basically, to

name media components for text, images,audio and video with URLs, and to schedule their presentation either in parallel or in sequence.

Quoting the SMIL 2.0 working draft, we can characterize the SMIL presentation characteristics as follows:

presentation characteristics

• The presentation is composed from several components that are accessible via URL's, e.g. files stored on a Web server.
• The components have different media types, such as audio, video, image or text. The begin and end times of different components are specified relative to events in other media components. For example, in a slide show, a particular slide is displayed when the narrator in the audio starts talking about it.
• Familiar looking control buttons such as stop, fast-forward and rewind allow the user to interrupt the presentation and to move forwards or backwards to another point in the presentation.
• Additional functions are "random access", i.e. the presentation can be started anywhere, and "slow motion", i.e. the presentation is played slower than at its original speed.
• The user can follow hyperlinks embedded in the presentation.

applications

• Photos taken with a digital camera can be coordinated with a commentary
• Training courses can be devised integrating voice and images.
• A Web site showing the items for sale, might show photos of the product range in turn on the screen, coupled with a voice talking about each as it appears.
• Slide presentations on the Web written in HTML might be timed so that bullet points come up in sequence at specified time intervals, changing color as they become the focus of attention.
• On-screen controls might be used to stop and start music.

   <par>
      <a href="#Story"> <img src="button1.jpg"/> </a>
      <a href="#Weather"> <img src="button2.jpg"/></a>
       <excl>
           <par id="Story" begin="0s">
             <video src="video1.mpg"/>
             <text src="captions.html"/>
           </par>
  
           <par id="Weather">
             <img src="weather.jpg"/>
             <audio src="weather-rpt.mp3"/>
           </par>
       </excl>
   </par>
  

Before discussing how the functionality proposed in the SMIL 2.0working draft may be realized, we might reflect on how to position SMIL with respect to the many other approaches to provide multimedia on the web. As other approaches we may think of flash, dynamic HTML (using javascript), or java applets. In the SMIL 2.0 working draft we read the following comment:

history

Experience from both the CD-ROM community and from the Web multimedia community suggested that it would be beneficial to adopt a declarative format for expressing media synchronization on the Web as an alternative and complementary approach to scripting languages.

Following a workshop in October 1996, W3C established a first working group on synchronized multimedia in March 1997. This group focused on the design of a declarative language and the work gave rise to SMIL 1.0 becoming a W3C Recommendation in June 1998.

In summary, SMIL 2.0 proposes a declarative format to describe the temporal behavior of a multimedia presentation, associate hyperlinks with media objects, describe the form of the presentation on a screen, and specify interactivity in multimedia presentations. Now,why such a fuzz about "declarative format"? Isn't scripting more exciting? And aren't the tools more powerful? Ok, ok. I don't want to go into that right now. Let's just consider a declarative format to be more elegant. Ok?

To support the functionality proposed for SMIL 2.0 the working draft lists a number of modules that specify the interfaces for accessing the attributes of the various elements. SMIL 2.0 offers modules for animation, content control, layout, linking, media objects, meta information, timing and synchronization, and transition effects.

SMIL 2.0 Modules

• The Animation Modules
• The Content Control Modules
• The Layout Modules
• The Linking Modules
• The Media Object Modules
• The Metainformation Module
• The Structure Module
• The Timing and Synchronization Module
• The Time Manipulations Module
• The Transition Effects Module

This modular approach allows to reuse SMIL syntax and semantics in other XML-based languages, in particular those that need to represent timing and synchronization. For example:

module-based reuse

• SMIL modules could be used to provide lightweight multimedia functionality on mobile phones, and to integrate timing into profiles such as the WAP forum's WML language, or XHTML Basic.
• SMIL timing, content control, and media objects could be used to coordinate broadcast and Web content in an enhanced-TV application.
• SMIL Animation is being used to integrate animation into W3C's Scalable Vector Graphics language (SVG).
• Several SMIL modules are being considered as part of a textual representation for MPEG4.

The SMIL 2.0 working draft is at the moment of writing being finalized. It specifies a number of language profiles topromote the reuse of SMIL modules. It also improves on the accessibility features of SMIL 1.0, which allows for, for example,, replacing captions by audio descriptions.

In conclusion, SMIL 2.0 is an interesting standard, for a number of reasons. For one, SMIL 2.0 has solid theoretical underpinnings in a well-understood, partly formalized, hypermedia model (AHM). Secondly, it proposes interesting functionality, with which authors can make nice applications. In the third place, it specifies a high level declarative format, which is both expressive and flexible. And finally, it is an open standard (as opposed to proprietary standard). So everybody can join in and produce players for it!

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(C) Æliens 18/6/2009

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