L. SMIL Timing and Synchronization

Previous version:
http://www.w3.org/AudioVideo/Group/Timing/smil-timing-990727.html (W3C members only)
Patrick Schmitz (Microsoft),
Warner ten Kate (Philips),
Ted Wugofski (Invited Expert, Gateway),
Jeff Ayars (RealNetworks), Bridie Saccocio (RealNetworks)


This is a working draft specification of timing and synchronization functionality for SMIL and other XML documents that incorporate SMIL Timing and Synchronization. It is part of the work in the Synchronized Multimedia Working Group (SYMM) towards a next version of the SMIL language (SMIL Boston) and associated modules. This version extends the Timing and Synchronization support available in the SMIL 1.0 specification.

Table of Contents

1.0 Introduction

SMIL 1.0 solved fundamental media synchronization problems and defined a powerful way of choreographing multimedia content. SMIL Boston extends the timing and synchronization support, adding capabilities to the timing model and associated syntax. This section of the document specifies the Timing and Synchronization module.

There are two intended audiences for this module: implementers of SMIL Boston document viewers or authoring tools, and authors of other XML languages who wish to integrate timing and synchronization support.

In the process of extending SMIL 1.0 for modularization and use in other XML languages, some alternate syntaxes have been defined. If a document would otherwise be SMIL 1.0 compatible except for use of alternate syntax, the use of the SMIL 1.0 syntax is recommended so the document will be playable by SMIL 1.0 as well as later document players.

As this module is used in different profiles, the associated syntax requirements may vary.  Differences in syntax should be minimized as much as is practical.  The semantics of the timing model and of the associated markup must remain consistent across all profiles.  Any document type that includes SMIL Boston Timing and Synchronization markup (either via a hybrid DTD or via namespace qualified extensions) must preserve the semantics of the model defined in this specification.

The specification of timing and synchronization is organized in the following way. Time model concepts are introduced first, followed by a normative description of the time model and time graph construction. Clarification is provided for aspects of the model that were insufficiently documented in SMIL 1.0. The associated SMIL-DOM interfaces are described next. Open issues and examples are separated into appendices for readability purposes.