Transcript W3C and SMIL - Petra Christian University

Synchronized Multimedia Interface
Language (SMIL) and W3C
Multimedia E-Commerce Course
November 20, 2000
Mike Christel and Alex Hauptmann
World Wide Web Consortium
• W3C, founded in October 1994: http://www.w3.org/
• Purpose: develop common protocols that promote
WWW’s evolution and ensure its interoperability, in part
by providing:
• A repository of information about the WWW for developers
and users, especially specifications about the web
• A sample code implementation to embody and promote
standards
• Various prototype and sample applications to demonstrate
use of new technology
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More on W3C
• Directed by Tim Berners-Lee, inventor of the WWW
• 481 members as of 11/18/2000 (370 Members as of
11/11/1999)
• vendor-neutral forum
• http://www.w3.org/Consortium/Member/List
• Specifications must be formally approved by the
membership via W3C Recommendation track
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W3C Recommendation Track
• Working Draft
Work in progress, commitment to pursue work in area
• Candidate Recommendation
Proposed for implementation experience and
feedback
• Proposed Recommendation
Sent to the Advisory Committee for review
• Recommendation
Consensus within W3C, appropriate for widespread
deployment and promote W3C's mission
(source: http://www.w3.org/Consortium/Process/)
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Some W3C Specifications
• User Interface Domain
Hypertext Markup Language (HTML), Cascading Style
Sheets (CSS), Document Object Model (DOM), SMIL
• Technology and Society Domain
Platform for Internet Content Selection (PICS), Resource
Description Framework (RDF), Platform for Privacy
Preferences (P3P)
• Architecture Domain
Hypertext Transfer Protocol (HTTP), Extensible Markup
Language (XML)
...Follow links at http://www.w3.org/ for more details…
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XML: A Quick Introduction
• XML is a method for putting structured data in a text file
extensible, support for internationalization/localization,
platform-independent
• XML makes use of tags in ‘<‘ ‘>’ but is not HTML
meaning of tags like “<p>” and attributes left to the
application that reads it
• XML is text, not binary, but is not meant to be read
XML has strict parsing rules; more verbose that binary but
zip/gzip, cheap storage, etc. minimize that disadvantage
• XML is license-free, platform-independent and wellsupported, a W3C standard since February 1998
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SMIL: Synchronized Multimedia
Integration Language
• SMIL 1.0 specification, June 15, 1998, available at:
http://www.w3.org/TR/REC-smil/
• W3C SMIL references available at:
http://www.w3.org/AudioVideo/
• Purpose: a new language for scheduling multimedia
presentations where audio, video, text and graphics are
combined in real-time
• Result: an XML application enabling authors to specify
what should be presented when
XML implies: extensible, support for internationalization and
localization, platform-independent, editable by hand, etc.
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SMIL 2.0
SMIL 2.0 has the following two design goals:
• Define an XML-based language that allows authors to
write interactive multimedia presentations. Using SMIL
2.0, an author can describe the temporal behavior of a
multimedia presentation, associate hyperlinks with
media objects and describe the layout of the
presentation on a screen.
• Allow reusing of SMIL syntax and semantics in other
XML-based languages, in particular those who need to
represent timing and synchronization. For example,
SMIL 2.0 components are used for integrating timing
into XHTML and into SVG.
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SMIL Timeline
Oct 1996: Workshop
Mar 1997: W3C working group on synchronized multimedia
Jun 1998: W3C Recommendation (SMIL 1.0)
Sep 1998: Timed Interactive Multimedia Extensions for
HTML (HTML+TIME), W3C Note
http://www.w3.org/TR/NOTE-HTMLplusTIME
Feb 1999: 2nd Working Group on Synchronized Multimedia
(SYMM) formed
http://www.w3.org/TR/NOTE-SYMM-modules
Aug 1999: First working draft (SMIL “Boston”) released
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SMIL Timeline, Continued
Dec 1999: Chinese Translation of SMIL 1.0
Jan 2000: Realslideshow 2.0 from RealNetworks
Jan 2000: Internet Explorer 5.5 Preview by Microsoft
(supports selected modules of SMIL “Boston” draft)
Jan 2000: Apple QuickTime 4.1 now a SMIL 1.0 player
http://www.w3.org/TR/NOTE-HTMLplusTIME
Jun 2000: Fourth Working Draft of SMIL “Boston”
released
Oct 20, 2000: Last call for comments on Public Working
Draft of SMIL 2.0
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SYMM-WG Contributors
Synchronized Multimedia Working
Group contributing organizations:
Compaq, CSELT, CWI, France
Telecom, Gateway, Glocomm, IBM,
INRIA, Intel, Macromedia, Microsoft,
Netscape/AOL, NIST, Nokia, Oratrix,
Panasonic, Philips, RealNetworks,
WGBH, W3C
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Example of Contributing Org. Agendas
• WGBH a contributor to Synchronized Multimedia Working
Group
• WGBH partner in CPB/WGBH National Center for
Accessible Media
http://main.wgbh.org/wgbh/pages/ncam/aboutncam.
html
• Agenda: “make media accessible to underserved
populations such as disabled persons…”
• “NCAM is currently working with the W3C to add to SMIL the ability to
pause the video track and play extended audio descriptions, which
will provide blind users with more information than would otherwise
be possible. This capability will be part of the next version of SMIL.”
http://main.wgbh.org/wgbh/pages/ncam/webaccess/pivot/pvtaxxmm.html
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SMIL 1.0 Modules
• Structure
• Meta (“who”, “what”)
• Layout (“where”)
• Timing and Synchronization (“when”)
• Media Elements (“what”)
• Linking
• Content Control
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SMIL High Level Document Structure
<smil>
<head>
<meta>
<!-- … information about the document … -->
</meta>
<layout>
<!-- … definitions used for the spatial layout … -->
</layout>
</head>
<body>
<!-- … objects, temporal relations, links … -->
</body>
</smil>
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SMIL 1.0 Structure
<smil>
<head>
</head>
<body>
</body>
</smil>
These elements used in documents based upon
traditional SMIL profiles.
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SMIL 1.0 Meta
<smil>
<head>
<meta … />
</head>
</smil>
The meta elements contain information describing the
document, either to inform the human user or to assist
some automation, e.g.,
<meta name="title" content=”My Italy Trip"/>
<meta name="copyright" content="©1998 WGBH" />
<meta name="base” content="http://billswin.edu/Italy/"/>
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SMIL 1.0 Layout
<smil>
<head>
<layout>
<root-layout … />
<region id=“R1” … />
<region id=“R2” … />
</layout>
</head>
</smil>
Includes the <layout>, <root-layout> and <region>
elements, and related attributes.
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SMIL 1.0 Layout Examples
<root-layout height="300" width="450" backgroundcolor="#FFFFFF" title="Venezia!"/>
<root-layout height="450" width="625" backgroundcolor="black"/>
<region id="title" left="5" top="150" width="400"
height="200" z-index="1"/>
<region id="videoregion" top="0" left="0" height="240"
width="352"/>
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SMIL 1.0 Timing and Synchronization
<smil>
<body>
<!-- … timing included here … -->
</body>
</smil>
• Sequence and parallel timelines, via <seq> and <par>
• Timing control properties, via “begin”, “end”, “repeat”,
“dur”
• “The accuracy of synchronization between the children
in a parallel group is implementation-dependent”
• “soft synchronization” vs. “hard synchronization”
• how to realize hard synchronization
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Hard vs. Soft Synchronization
• Hard synchronization: player synchronizes the children
in the "par" (parallel play) element to a common clock
• Soft synchronization: each child of the "par" element
has its own independent clock
audio
video
audio
video
Hard sync. case 1: stop audio, e.g.,
wait to regain lip synchronization
Hard sync. case 2: drop video
frames, e.g., narrative
audio
video
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Soft sync: audio unaffected
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SMIL 2.0 New Focus on Sync. Behavior
<par>
<animation src="..." />
...
<par id="speech" syncBehavior="canSlip" >
<video src="speech.mpg" syncBehavior="locked" />
<audio src="speech.au" syncBehavior="locked" />
</par>
...
</par>
There is also a syncTolerance that is referenced when
syncBehavior is “locked”, to ignore a given amount of
slew without forcing resynchronization
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SMIL 1.0 Media Elements
<smil>
<body>
<!-- … media elements included here … -->
</body>
</smil>
• Includes the media declaration elements <text>, <img>,
<audio>, <video>, <textstream>, <animation>, and
<ref>
• all absolutely positioned elements (animation, img, ref,
text, textstream and video) are contained within a single
containing block defined by the root-layout element
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SMIL 1.0 Linking
<smil>
<body>
<!-- … linking included here … -->
</body>
</smil>
• Includes the <a> and <anchor> elements, e.g.,
<a href="http://www.w3c.org" >
<text src="media/w3c.txt" region="w3c”
begin="14.05s" dur="15.95s" />
</a>
• Timing applied to HTML <a> and <area> tags could
provide much or all of SMIL functionality; hence, linking
modules under review
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SMIL 1.0 Content Control
<smil>
<head>
<!-- … switch element can be used here … -->
</head>
<body>
<!-- … switch element can be used here too … -->
</body>
</smil>
Content control based on “<switch>” and test attributes:
system-bitrate, system-captions, system-language, systemoverdub-or-caption, system-required, system-screen-size,
system-screen-depth
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