The first W3C Working Group on Synchronized Multimedia (SYMM) developed SMIL, the Synchronized Multimedia Integration Language [SMIL10]. This XML-based language [XML10] is used to express timing relationships among media elements such as audio and video files. SMIL 1.0 documents describe multimedia presentations that can be played in a SMIL-conformant viewer.
Since the publication of SMIL 1.0, interest in the integration of SMIL concepts with the HTML, the Hypertext Markup Language [HTML40], and other XML languages, has grown. Likewise, the W3C HTML Working Group is exploring how XHTML, the Extensible Markup Language [XHTML10], can be integrated with other languages. Both Working Groups are considering modularization as a strategy for integrating their respective functionality with each other and other XML languages.
Modularization is a solution in which a language's functionality is partitioned into sets of semantically-related elements. Profiling is the combination of these feature sets to solve a particular problem. For the purposes of this specification we define:
SMIL functionality is partitioned into modules based on the following design requirements:
The first requirement is that modules are specified such that a collection of modules can be "recombined" in such a way as to be backward compatible with SMIL (it will properly play SMIL conforming content).
The second requirement is that the semantics of SMIL must not change when they are embodied in a module. Fundamentally, this ensures the integrity of the SMIL content and timing models. This is particularly relevant when a different syntax is required to integrate SMIL functionality with other languages.
The third requirement is that modules be isomorphic with other modules from other W3C recommendations. This will assist designers when sharing modules across profiles.
The fourth requirement is that specific attention be paid to providing multimedia functionality to the XHTML language. XHTML is the reformulation of HTML in XML.
The fifth requirement is that the modules should adopt new W3C recommendations when they are appropriate and when they do not conflict with other requirements (such as complementing the XHTML language).
The sixth requirement is to ensure that modules have integrated support for the document object model. This facilitates additional control through scripting and user agents.
These requirements, and the ongoing work by the SYMM Working Group, led to a partitioning of SMIL functionality into nine modules.
SMIL functionality is partitioned into nine (9) modules :
Each of these modules introduces a set of semantically-related elements, properties, and attributes.
The Animation Module provides a framework for incorporating animation onto a timeline (a timing model) and a mechanism for composing the effects of multiple animations (a composition model). The Animation Module defines semantics for the animate, set, animateMotion, and animateColor elements.
The Content Control Module provides a framework for selecting content based on a set of test attributes. The Content Control Module defines semantics for the switch element.
The Layout Module provides a framework for spatial layout of visual components. The Layout Module defines semantics for the layout, root-layout, and region elements.
The Linking Module provides a framework for relating documents to content, documents and document fragments. The Linking Module defines semantics for the "a" and "area" elements.
The Media Object Module provides a framework for declaring media. The Media Object Module defines semantics for the ref, animation, audio, img, video, text, and textstream elements.
The Metainformation Module provides a framework for describing a document, either to inform the human user or to assist in automation. The Metainformation Module defines semantics for the meta element.
The Structure Module provides a framework for structuring a SMIL document. The Structure Module defines semantics for the smil, head, and body elements.
The Timing and Synchronization Module provides a framework for describing timing structure, timing control properties, and temporal relationships between elements. The Timing and Synchronization Module defines semantics for par, seq, and excl elements. In addition, this module defines semantics for properties including begin, dur, end, repeatCount, repeatDur, et al. These elements and attributes are subject to change.
The Transition Effects Module defines a taxonomy of transition effects as well as semantics and syntax for integrating these effects into XML documents
A requirement for SMIL modularization is that the modules be isomorphic with other modules from other W3C recommendations. Isomorphism will assist designers when sharing modules across profiles.
| Animation | animate, set, animateMotion, animationColor | - | - |
| Content Control | switch | - | - |
| Layout | layout, region, root-layout | Stylesheet | style |
| Linking | a, area | Hypertext | a |
| Link | link | ||
| Base | base | ||
| Image Map | map, area | ||
| Media Object | ref, audio, video, text, img, animation, textstream | Object | object, param |
| Image | img | ||
| Applet | applet, param | ||
| Metainformation | meta | Metainformation | meta |
| Structure | smil, head, body | Structure | html, head, body, title |
| Timing and Synchronization | par, seq, excl | - | - |
| Transition Effects | transition | - | - |
As can be seen in the table, the Metainformation module appears in both SMIL and HTML. Work is underway to define a single module that can be shared by both SMIL and HTML.
There are a range of possible profiles that may be built using SMIL modules. Four profiles are defined to inform the reader of how profiles may be constructed to solve particular problems:
These example profiles are non-normative.
The Lightweight Presentations Profile handles simple presentations, supporting timing of text content. The simplest version of this could be used to sequence stock quotes or headlines on constrained devices such as a palmtop device or a smart phone. This example profile might include the following SMIL modules:
This profile may be based on XHTML modules [XMOD] with the addition of Timing and Synchronization Module.
The SMIL-Boston Profile supports the timeline-centric multimedia features found in SMIL language. This profile might include the following SMIL modules:
The XHTML Presentations Profile integrates multimedia, XHTML layout, and CSS positioning. This profile might include the following SMIL modules:
This profile would use XHTML modules for structure and layout and SMIL modules for multimedia and timing. The linking functionality may come from the XHTML modules [XMOD] or from the SMIL modules.
The Web Enhanced Media Profile supports the integration of multimedia presentations with broadcast or on-demand streaming media. The primary media will often define the main timeline. This profile might include the following SMIL modules:
This profile is similar to the XHTML Presentations Profile with additional support to manage stream events and synchronization of the document's clock to the primary media.