Work on Synchronized Multimedia is being managed as part of W3C's Architecture Domain.
Activity statements provide a managerial overview of W3C's work in this area. They are designed to be read from beginning to end, to be informative and interesting. The role of W3C is given, also the benefits to the Web community, accomplishments to date and a summary of what the future holds. Background reading pages to help set the scene and explain any technical concepts are in preparation. Where necessary these also contain a short tutorial.
The Web is fast-evolving beyond the limits of simple pages of text and images. W3C is focussing on the design of a new language for scheduling multimedia presentations where audio, video, text and graphics are combined in real-time. Synchronized Multimedia Integration Language (SMIL), enables authors to specify what should be presented when. You can, for example, control the precise time that a sentence is spoken and make it coincide with the display of a given image.
Web technology has until now, been limited when it comes to creating continuous multimedia presentations. For this, two new components need to be added to Web technology: a format for authoring synchronized multimedia content, and support for network transmission of this type of content.
One way to schedule the presentation of each media component is to use a scripting language, such as Macromedia's Lingo or Apple's Hypercard. On the Web, you could use JavaScript (ECMAScript) or VBScript (derived from Visual Basic). The downside is that such scripts are hard to maintain and don't lend themselves to simple authoring tools. As a result, CD-ROM authoring tools tend to use declarative formats such as Apple's Quicktime.
Experience from both the CD-ROM community and from the Web community suggests 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 working group on synchronized multimedia in March 1997. This group has focussed on the design of a declarative language for scheduling multimedia presentations on the Web named the "Synchronized Multimedia Integration Language". It is generally referred to using the abbreviation "SMIL" (pronounced "smile"). SMIL is an application of XML.
Philipp Hoschka is the Chair of the Synchronized Multimedia Working Group - SYMM (W3C members only) and editor of the SMIL specification. The working group was established in March 1997. There is a SMIL Mailing list for discussing all aspects of real-time multimedia on the Web. The list's Archive is open to all interested persons. To subscribe:
The basic idea is to name media components for text, images, audio and video with URLs and to schedule their presentation either in parallel or in sequence. A typical SMIL presentation has the following characteristics:
SMIL has been designed so that it is easy to author simple presentations with a text editor. The key to success for HTML was that attractive hypertext content could be created without requiring a sophisticated authoring tool. SMIL achieves the same goal for synchronized hypermedia.
Transmitting synchronized multimedia content over the Internet requires meeting the real-time constraints of the presentation - a particular piece of a file has to available when it is needed in the presentation. There are two solutions for addressing this issue: prefetching of files and using a streaming protocol. The Web protocol HTTP is fine for prefetching files but poorly suited to streaming audio and video. W3C is focussing on two streaming protocols:
The Real Time Transport Protocol (RTP) is the standard protocol for streaming applications developed within the IETF.
The Real-Time Streaming Protocol (RTSP) protocol is currently being discussed by the IETF. It provides methods to realize commands similar to the functionality provided by a CD player or a video recorder, such as play, fast-forward, pause, stop and record. RTSP shares many properties with HTTP. The motivation is to reuse technology that has been developed for HTTP (caching of content, authentication, encryption, PICS) when accessing real-time multimedia content. W3C is thus carefully tracking the development of RTSP.
The Synchronized Multimedia Integration Language (SMIL) 1.0 Specification was released on the 15 June 1998 as a W3C Recommendation, representing cross-industry agreement on a wide range of features for putting multimedia presentations on the Web.
This is presently under consideration by the Director of W3C, but is expected to involve closer integration with other XML tag sets being developed by W3C.
W3C is holding a workshop in late June on Television and the Web to foster a better understanding of the requirements for next steps.
Philipp Hoschka, Synchronized Multimedia Activity lead
Last modified $Date: 1998/06/22 14:49:11 $