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8. The SMIL Metadata Module

Thierry Michel (, W3C

Table of contents

8.1 Introduction

The World Wide Web was originally built for human consumption, and although everything on it is machine-readable, this data is not machine-understandable. It is very hard to automate anything on the Web, and because of the volume of information the Web contains, it is not possible to manage it manually. Metadata is "data about data" (for example, a library catalog is metadata, since it describes publications) or specifically in the context of this specification "data describing Web resources".
The solution proposed here is to use metadata to describe SMIL documents published on the Web.

The earlier SMIL 1.0 specification allowed authors to describe documents with a very basic vocabulary using the "meta" element.
The SMIL Metadata module defined in this specification fully supports the use this "meta" element from SMIL 1.0 but it also introduces new capabilities for describing metadata using the Resource Description Framework Model and Syntax [RDFsyntax], a powerful metadata language for providing information about resources.

8.2 Compatibility with SMIL 1.0 using the meta Element

To insure backward compatibility with SMIL 1.0, the  <meta> element as specified in the SMIL 1.0 [SMIL10] Recommendation can be used to define properties of a document (e.g., author/creator, expiration date, a list of key words, etc.) and assign values to those properties.
Each <meta> element specifies a single property/value pair in the name and content attributes, respectively.

8.2.1 Element Attributes

The "meta" element can have the following attributes:

This attribute specifies the value of the property defined in the meta element.
The "content" attribute is required for "meta" elements.
This attribute uniquely identifies an element within a document. Its value is an XML identifier.
This attribute identifies the property defined in the meta element.
The "name" attribute is required for "meta" elements.
This attribute is introduced for future extensibility of SMIL. It is interpreted in the following two cases:
  • If a new element is introduced in a future version of SMIL, and this element allows SMIL 1.0 elements as element content, the "skip-content" attribute controls whether this content is processed by a SMIL 1.0 player.
  • If an empty element in SMIL version 1.0 becomes non-empty in a future SMIL version, the "skip-content" attribute controls whether this content is ignored by a SMIL 1.0 player, or results in a syntax error.
If the value of the "skip-content" attribute is "true", and one of the cases above apply, the content of the element is ignored. If the value is "false", the content of the element is processed.
The default value for "skip-content" is "true".

The list of properties is open-ended. This specification defines the following properties:

The value of this property determines the base URI for all relative URIs used in the document.
pics-label or PICS-Label
The value of this property specifies a valid rating label for the document as defined by PICS [PICS].
The value of this property contains the title of the presentation.

This specification extends the SMIL 1.0 "meta" element with the following attributes:

[I18N] xml:lang
This attribute specifies the language used.
This attribute may be used in place of the name attribute. HTTP servers use this attribute to gather information for HTTP response message headers.
This attribute names a scheme to be used to interpret the property's value.

8.2.2 Element Content

The "meta" element is an empty element.

8.3 Extensions to SMIL 1.0 Metadata.

RDF  provides a more general treatment of metadata. RDF is a declarative language and provides a standard way for using XML to represent metadata in the form of statements about properties and relationships of items on the Web. Such items, known as resources, can be almost anything, provided it has a Web address. This means that you can associate metadata with a SMIL documents, but also a graphic, an audio file, a movie clip, and so on.

RDF is the appropriate language for metadata. The specifications for RDF can be found at:

Metadata within an SMIL document should be expressed in the appropriate RDF namespaces [XML-NS] and should be placed within the <metadata> child element to the document's <smil> root element. (See example below.)

8.3.1 Element Attributes

The "metadata" element can have the following attributes:

This attribute uniquely identifies an element within a document. Its value is an XML identifier.

8.3.2 Element Content

The "metadata" element can contain the following child elements:

<RDF> element and its sub-elements.

8.3.3 Using multiple description schemes simultaneously

RDF appears to be the ideal approach for supporting descriptors from multiple description schemes simultaneously.

Here are some suggestions for content creators regarding metadata:

Individual industries or individual content creators are free to define their own metadata schema, but everyone is encouraged to follow existing metadata standards and use standard metadata schema wherever possible to promote interchange and interoperability. If a particular standard metadata schema does not meet your needs, then it is usually better to define an additional metadata schema in RDF that is used in combination with the given standard metadata schema than to totally avoid the standard schema.

8.4 The SMIL Metadata Schema

(This schema has not yet been defined. Here are some candidate attributes for the schema: LevelAccessibilityGuidelines, ListOfImagesUsed, ListOfAudioUsed, ListOfTextUsed, ListOfTextstreamUsed, ListOfRefUsed, ListOfCodecUsed, etc)

8.5 An Example

Here is an example of how metadata can be included in an SMIL document. The example uses the Dublin Core  version 1.0 Schema  [DC] and the SMIL Metadata Schema:

<?xml version="1.0" ?>
<smil xmlns = "">
 <meta id="meta-smil1.0-a" name="Publisher" content="W3C" />
 <meta id="meta-smil1.0-b" name="Date" content="1999-10-12" />
 <meta id="meta-smil1.0-c" name="Rights" content="Copyright 1999 John Smith" />

  <metadata id="meta-rdf">
       xmlns:rdf = ""
       xmlns:rdfs = ""
       xmlns:dc = ""
       xmlns:smilmetadata = "" >

<!-- Metadata about the SMIL presentation -->
   <rdf:Description about=""
       dc:Title="An Introduction to the Resource Description Framework"
       dc:Description="The Resource Description Framework (RDF) enables the encoding, exchange and reuse of structured metadata"
       dc:Rights="Copyright 1999 John Smith"
       dc:Format="text/smil" >                
          <rdf:Seq ID="CreatorsAlphabeticalBySurname">
             <rdf:li>Mary Andrew</rdf:li>
             <rdf:li>Jacky Crystal</rdf:li>
          <rdf:Seq ID="VideoAlphabeticalByFormatname">
              <rdf:li Resource=""/>
              <rdf:li Resource=""/> 
       <smilmetadata:Access LevelAccessibilityGuidelines="AAA"/>

<!-- Metadata about the video -->
   <rdf:Description about=""
        dc:Title="RDF part one"
        dc:Creator="John Smith"
        dc:Description="RDF basic fonctionalities"
        dc:Publisher="W3C Press Service"
        smilmetadata:Duration="60 secs"
        smilmetadata:VideoCodec="MPEG2" >
           <rdf:Seq ID="ChronologicalSequences">
             <rdf:li Resource=""/>
             <rdf:li Resource=""/> 

<!-- Metadata about a scene of the video -->
   <rdf:Description about="#scene1"
        dc:Title="RDF intro"
        dc:Description="Introduction to RDF fonctionalities"
        smilmetadata:Duration="30 secs"
        smilmetadata:Presenter="David Jones" >
           <rdf:Seq ID="ChronologicalShots">

<!-- SMIL presentation -->
    <region id="a" top="5" />
   <video region="a" src="/videos/meta-1999.mpg" >
     <area id="scene1" begin="0" end ="30"/>
     <area id="scene2" begin="30" end ="60"/>
   <video region="a" src="/videos/meta2-1999.mpg"/>

Note:Validate the above RDF description with SiRPAC; a Simple RDF Parser and Compiler, written by Janne Saarela (W3C).

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