SMIL for multimedia presentations.
What Is Streaming Media?
Streaming media is a technology for transferring and displaying audio, video, and other multimedia data in real time over the Internet or private networks. Streaming media's objective is to process and display the media objects seamlessly, as a steady and continuous stream, when the Web page that contains it is downloaded to a user's system. However, that system must have an appropriate player application (that is, a viewer or plug-in) installed on it to display the media data objects.
Streaming results in little or no initial delay between the download action and the display and no delay as additional data is downloaded. The recipient's viewer application actually displays the data before the file transmission is completed. Streaming is especially beneficial when users cannot download large multi-media files quickly. Prior to streaming, users had to download one or more files to their hard disk drives and then, after the files were completely down-loaded, they could play them. With streaming, almost any user can enjoy a Web page's contents immediately after selecting it.
The three common methods for delivering streaming media are:
* True streaming. This is the latest trend. It requires a separate server for the streaming media and a media viewer application that is specific to the format of the requested media.
* HTTP streaming. Also called progressive download streaming, or serverless streaming, HyperText Transfer Protocol streaming was the first popular form. It uses a standard Web server, not a separate dedicated streaming server, but it also needs a specific media player application.
* Clientless streaming. For this technology, the viewer application is provided during the streaming process. As streaming media has become almost commonplace, it has created a demand for better media creation tools.
Consequently, a number of competing streaming technologies and standards have been developed.
What Is the Synchronized Multimedia Integrated Language?
The Synchronized Multimedia Integration Language (SMIL, pronounced "smile") is an XML application that enables you to create multimedia data presentations and integrate them with the text and graphics on Web sites. It was developed specifically to integrate multimedia presentations while optimizing bandwidth.
SMIL provides several capabilities, including the following:
* The integration of text, image, audio, and video media.
* Control of visual media layout.
* Control of synchronization (also called the temporal behavior) of the various media.
* The creation of hyperlinks to include additional media (for example, to jump to another part of the presentation, initiate a new presentation, or open another Web page.
* Local or remote storage of the media content.
* The ability to search SMIL files for component names or text strings. SMIL files are really just text files.
* The division of multimedia content into separate streams for individual transmission, without sacrificing the integrated display aspect.
* The ability to adapt media streams to match the recipient system characteristics. For example, media objects can be created and stored in multiple versions to facilitate transmission or display, or to accommodate different language soundtracks.
* Reuse of any or all media objects in multiple presentations, because each object is accessed with a unique URI.
SMIL differs from Java, which has had multimedia capability for a long time. But SMIL's human-legibility makes it easier for non-Java programmers to use. Meanwhile, SMIL documents can still be assembled on the fly by Java servlets or CGI scripts.
Recently, the W3C endorsed the more powerful, more sophisticated, and much larger SMIL 2.0 Recommendation; but because this is an introductory level discussion, SMIL 1 .0's principles are sufficient to provide a basic understanding of the technology.
The W3C and SMIL
The W3C's SMIL Recommendations have been prepared by the Synchronized Multimedia Working Group (SYMM-WG), which over the years has included representatives from the following organizations: Alcatel, Apple, CNET/DSM, Canon, Compaq, CSELT, CWI, DAISY Consortium, DEC, Ericsson, France Telecom, Gateway, Glocomm, GMD, Havas, IBM, INRIA, Intel, Lucent/Bell Labs, Macromedia, Microsoft, Netscape/AOL, NIST, Nokia, Oratrix, Pana sonic, Philips, The Productivity Works, RealNetworks, WGBH, and the W3C. The first Working Group was assembled in January 1997. It published a public draft of SMIL 1.0 in November 1997. Development has continued since then
The full.specification of SMIL 1.0, Synchronized Multimedia Integration Language (SMIL) 1.0 Specification, was endorsed as a W3C Recommendation in June 1998. Microsoft contributed to SMIL 1.0 development up until the last draft, but it did not embrace the SMIL 1.0 Recommendation. Microsoft said that SMIL 1.0 overlapped with several existing standards, for example, CSS2, HTML, and the XML Document Object Model (DOM), and was unnecessary. Macromedia did not embrace SMIL because it claimed that SMILs features were not sophisticated enough. Macromedia also believed that SMIL overlapped and potentially conflicted with existing standards, most notably the XML DOM.
The SYMM Working Group also produced Synchronized Multimedia Integration Language (SMIL) 2.0, which was endorsed as a W3C Recommendation in August 2001. It is approximately 10 times larger than SMIL 1.0 and, unlike SMIL 1.0, consists of sets of markup modules. Each module defines the semantics and syntax for nine types of SMIL functionality: animation, content control, layout, linking, media objects, metainformation, structure, timing, and transition effects. Several of these functions are new, compared to SMIL 1.0, and were provided in response to developer requests. The modules can be used alone or in combination (for example, event-based interaction and transition effects can be combined). As you can see in Figure 1 SMIL 2.0 has nine DTDS, one for each module type, and/or 11 schemas that govern the same functionality. By comparison, the older and less sophisticated SMIL 1.0 uses only one DTD. The references to the appropriate validation documents (DTDs or schemas) are specified in the DOCTYPE definitions of the respective documents.
This profile, published as a W3C Note, describes the SMIL modules that are added to XHTML to add timing, animation, and multimedia functionality to XHTML elements. The profile supports all of the modules defined in the April 2001 W3C Recommendation rifled Modularization of XHTML.
The Note was produced by the SYMM Working Group and published by the W3C in late January 2002. It is made available for discussion only, and its publication indicates no endorsement by W3C, the SYMM Working Group, or any W3C members. Comments are welcome, but there is no guarantee of any action stemming from the comments, or even a reply.
Meanwhile, as a specification, the Note revises a previous Working Draft of the same title previously available in, but now removed from, SMIL 2.0. The profile includes several XHTML modules and SMIL 2.0 modules governing the following functionality: animation, content control, media objects, timing and synchronization, time manipulation, and transition effects. It also integrates these features with XHTML and CSS and describes how SMIL can be used to manipulate XHTML and CSS features. It also explains why the SMIL 2.0 layout, linking, structure, and metainformation modules were not included.
* SMIL 1.0 can be viewed at wwww3.org/TR/REC.smil/ and SMIL 2.0 at www.w3.org/TR/smil20/. The XHTML+SMIL profile is at wwww3.org/ TR/XI-ITMLplusSMIL/.
Viewing and Creating SMIL Documents
We suggest visiting the W3C's Synchronized Multimedia Web site at wwww3.Org/AudioVideo/for links to SM/L-related features, including the following:
* SMIL definitions and specifications
* Recent and past news articles
* Tutorials and other information sources
* Players, listed according to the two SMIL versions to SMIL authoring tools to Demonstrations
From XML in 60 Minutes in a Day, Wiley Publishing Inc, ISBN 0-471-42254-1
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|Title Annotation:||Standards--Electronic Business; Synchronized Multimedia Integration Language|
|Publication:||Database and Network Journal|
|Date:||Apr 1, 2004|
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