SMIL 2.0. Synchronized Multimedia Integration Language. Espen Nilsen

Transcription

1 SMIL 2.0 Synchronized Multimedia Integration Language Espen Nilsen Outline Introduction Design goals Structure and timelines Timing and Syncronization Events and Hyperlinking Content Control 1

2 Introduction Format for encoding multimedia presentations for delivery over the Web Collection of XML elements and attributes used to describe temporal and spatial coordinates of media objects User define how objects should be integrated in a presentation 10 major functional groupings of elements and attributes Timing and Synchronization are the core elements 2

3 Design goals Extend SMIL 1.0 functionality Increased interaction Enhanced timing semantics Extended content control and layout facilites New primitives: animation and transition Maintain declarative XML format Declarative rather than procedural format Means it doesn t define how to implement a presentation, this is left up to the player Introduce a module based structure More than 50 modules in 13 functional groups (500+ page spec) Allows integration of SMIL in other XML-based languages Structure A SMIL presentation is a structured composition of autonomous media objects Three basic timing containers seq : sequential Successor child can t begin before predesessor ends par : parallel Children rendered in parallel excl : exclusive Only one child can be active at a time... event based start condition Containers can be nested These elements form parent timing containers in which we can place media objects or other timing containers 3

4 Structure Timelines Timelines essentially useless since for excl activation and termination times are unknown and for par unresolved begin and end times This gives SMIL documents unprecedented temporal flexibility and adaptability because effective presentation timelines is determined at runtime In a SMIL presentation the objects structured composition determines the timeline rather than the timeline being the basic compositional unit 4

5 Timing Developed to answer issues related to timing: When does an element begin? How long is it active? What happens to it after that? Core of SMIL 2.0 s functionality Consist of 19 modules Timing Begin and End attributes Multiple begin/end values allowed Possible to mix both scheduled and event-based activation/termination in one attribute Ex: begin= 3s; button.activateevent Duration attribute 5

6 Synchronization Not ensured that all players have implemented all defined timing attributes in a specification SMIL provides 3 high-level synchronization control attributes syncbehavior Defines whether there can be slippagein implementing the presentations composite timeline synctolerance Defines how much slippage is allowed syncmaster Defines one element as the master timebase against which all others are measured Events and Hyperlinking Normally a documents activation hierarchy determines the rendering of document elements Users can influence this through events Powerful mechanism for conditional content activation The fundamental concept of the SMIL link is that it models a temporal seek in a presentation The target play state is identical to the state it would be in if it had arrived by playing it out This means that all nodes between the links source and destination must be evaluated Difficult to implement 6

7 Content control One of the major innovations in SMIL 2.0 Support for conditional content via the switch element E.g one can switch between video or sequence of images depending on system bitrate New in SMIL 2.0 is that users can define own set s of test attributes Both event mechanism and content control facilities provide a means for dynamically selecting objects in a presentation The basic difference events work on objects that the SMIL 2.0 scheduler recognizes, content control facilities determine which objects the scheduler gets to evaluate References SMIL 2.0 specification Article SMIL 2.0: Part 1: Overview, Concepts and Structure (Dick C.A. Bulterman) 7