Network Working Group                                         P. Hoschka
Request for Comments: 4536                                           W3C
Category: Informational                                         May 2006


      The application/smil and application/smil+xml Media Types

Status of This Memo

  This memo provides information for the Internet community.  It does
  not specify an Internet standard of any kind.  Distribution of this
  memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2006).

Abstract

  This document specifies the media type for versions 1.0, 2.0, and 2.1
  of the Synchronized Multimedia Integration Language (SMIL 1.0, SMIL
  2.0, SMIL 2.1).  SMIL allows integration of a set of independent
  multimedia objects into a synchronized multimedia presentation.

1.  Introduction

  The World Wide Web Consortium (W3C) has issued specifications that
  define versions 1.0 [1], 2.0 [2] and 2.1 [3] of the Synchronized
  Multimedia Integration Language (SMIL).  This memo provides
  information about the application/smil and application/smil+xml media
  types.

  The definition is based on RFC 3023, which defines the use of the
  "application/xml" media type [4].  Before using the
  "application/smil" or "application/smil+xml" media type, implementors
  must thus be familiar with [4].

2.  Synchronized Multimedia Integration Language

  SMIL allows integrating a set of independent multimedia objects into
  a synchronized multimedia presentation.  Using SMIL, an author can

  1. describe the temporal behavior of the presentation,
  2. describe the layout of the presentation on a screen,
  3. associate hyperlinks with media objects, and
  4. define conditional content inclusion/exclusion based on
     system/network properties.




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3.  Registration Information

3.1.  Registration of MIME media type application/smil

  MIME media type name: application

  MIME subtype name: smil

  Required parameters: none

  Optional parameters:

     charset

        Same as charset parameter considerations of application/xml in
        RFC 3023.

     profile

        See Section 5 of this document.

  Encoding considerations:

     Same as encoding considerations of application/xml in RFC 3023

  Security considerations: See Section 6, "Security Considerations", of
  this document.

  Interoperability considerations:

     SMIL documents contain links to other media objects.  The SMIL
     player must be able to decode the media types of these media in
     order to display the whole document.  To increase
     interoperability, SMIL has provisions for including alternate
     versions of a media object in a document.

  Published specification: See [1], [2], and [3]

  Applications which use this media type:

     SMIL players and editors










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  Additional information:

     Semantics of fragment identifiers in URIs: The SMIL media type
     allows a fragment identifier to be appended to a URI pointing to a
     SMIL resource (e.g., http://www.example.com/test.smil#foo).  The
     semantics of fragment identifiers for SMIL resources are defined
     in the SMIL specification.

  Magic number(s):

     There is no single initial byte sequence that is always present
     for SMIL files.  However, Section 4 of this document gives some
     guidelines for recognizing SMIL files.

  File extension(s): .smil, .smi, .sml

  NOTE: On the Windows operating system and the Macintosh platform, the
  ".smi" extension is used by other formats.  To avoid conflicts, it is
  thus recommended to use the extension ".smil" for storing SMIL files
  on these platforms.

  Macintosh File Type Code(s): "TEXT", ".SMI", "SMIL"

  Object Identifier(s) or OID(s): none

  Person & email address to contact for further information:

  The author of this memo.

  Intended usage: OBSOLETE

  Author/Change controller:

  The SMIL specification is a work product of the World Wide Web
  Consortium's SYMM Working Group.

  The W3C has change control over the specification.














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3.2.  Registration of MIME media type application/smil+xml

  MIME media type name: application

  MIME subtype name: smil+xml

  Required parameters: See registration of application/smil.

  Optional parameters: See registration of application/smil.

  Encoding considerations: See registration of application/smil.

  Security considerations: See Section 6, "Security Considerations", of
  this document

  Interoperability considerations: See registration of
  application/smil.

  Published specification: See registration of application/smil.

  Applications which use this media type: See registration of
  application/smil.

  Additional information: See registration of application/smil.

  Magic number(s): See registration of application/smil.

  File extension(s): See registration of application/smil.

  Macintosh File Type Code(s): See registration of application/smil.

  Object Identifier(s) or OID(s): See registration of application/smil.

  Person & email address to contact for further information: See
  registration of application/smil.

  Intended usage: COMMON

  Author/Change controller: See registration of application/smil.












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4.  Recognizing SMIL Files

  All SMIL files will have the string "<smil" near the beginning of the
  file.  Some will also begin with an XML declaration that begins with
  "<?xml", though that alone does not indicate a SMIL document.

  All SMIL 2.0 files must include a declaration of the SMIL 2.0
  namespace.  This should appear shortly after the string "<smil", and
  should read 'xmlns="http://www.w3.org/2001/SMIL20/Language"'.

  All SMIL 2.1 files must include a declaration of a SMIL 2.1
  namespace, appearing shortly after the string "<smil".  The namespace
  string depends on the language profile.  Please refer to the SMIL 2.1
  specification for the definition of the relevant namespace names.

5.  The "profile" Optional Parameter

  This parameter is meant to be used in MIME media-type-based content
  negotiation (such as that done with the HTTP "Accept" header) to
  negotiate for a variety of SMIL-based languages.  It is modelled
  after the "profile" parameter in the application/xhtml+xml MIME type
  registration [5] and is motivated by very similar considerations.

  The parameter is intended to be used only during content negotiation.
  It is not expected that it be used to deliver content, or that origin
  web servers have any knowledge of it (though they are welcome to).
  It is primarily targeted for use on the network by proxies in the
  HTTP chain that manipulate data formats (such as transcoders).

  The value of the profile attribute is a URI that can be used as a
  name to identify a language.  Though the URI need not be resolved in
  order to be useful as a name, it could be a namespace, schema, or
  language specification.

  For example, user agents supporting only SMIL Basic (see
  http://www.w3.org/TR/smil20/smil-basic.html) currently have no
  standard means to convey their inability to fully support SMIL 2.0.
  While SMIL 2.0 Basic user agents are required to parse the full SMIL
  2.0 language, there is potentially a substantial burden in receiving
  and parsing document content that will not be presented to the user,
  since its functionality is not included in SMIL Basic.

  In the future, the functionality afforded by this parameter will also
  be achievable by the emerging work on a protocol to transfer
  Composite Capability/Preferences Profiles (CC/PP) descriptions [6].
  It is suggested that the "profile" parameter be used until the CC/PP
  protocol work has been finalized.




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  An example use of this parameter as part of a HTTP GET transaction
  would be:

       Accept: application/smil+xml;
          profile="http://www.w3.org/2001/SMIL20/HostLanguage"

6.  Security Considerations

  SMIL documents contain a construct that allows "infinite loops".
  This is indispensable for a multimedia format.  However, SMIL clients
  should foresee provisions such as a "stop" button that lets users
  interrupt such an "infinite loop".

  As with HTML, SMIL documents contain links to other media (images,
  sounds, videos, text, etc.), and those links are typically followed
  automatically by software, resulting in the transfer of files without
  the explicit request of the user for each one.  The security
  considerations of each linked file are those of the individual
  registered types.

  The SMIL language contains "switch" elements.  SMIL provides no
  mechanism that ensures that the media objects contained in a "switch"
  element provide equivalent information.  An author knowing that one
  SMIL player will display one alternative of a "switch" and another
  will display a different part can put different information in the
  two parts.  While there are legitimate use cases for this, it also
  gives rise to a security consideration: The author can fool viewers
  into thinking that the same information was displayed when in fact it
  was not.

  In addition, all of the security considerations of RFC 3023 also
  apply to SMIL.



















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7.  Normative References

  [1]  "Synchronized Multimedia Integration Language (SMIL) 1.0
       Specification", W3C Recommendation REC-smil-19980615,
       http://www.w3.org/TR/1998/REC-smil/, July 1998.

  [2] "Synchronized Multimedia Integration Language (SMIL 2.0) -
       [Second Edition]", W3C Recommendation,
       http://www.w3.org/TR/2005/REC-SMIL2-20050107/, January 2005.

  [3] "Synchronized Multimedia Integration Language (SMIL 2.1)", W3C
       Recommendation, http://www.w3.org/TR/2005/REC-SMIL2-20051213/,
       December 2005.

  [4]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", RFC
       3023, January 2001.

8.  Informative References

  [5]  Baker, M. and P. Stark, "The 'application/xhtml+xml' Media
       Type", RFC 3236, January 2002.

  [6]  H. Ohto, J. Hjelm, G. Klyne, M. Butler, L. Tran, F. Reynolds, C.
       Woodrow "Composite Capability/Preferences Profiles (CC/PP):
       Structure and Vocabularies 1.0", W3C Recommendation
       http://www.w3.org/TR/CCPP-struct-vocab/, January 2004.

Author's Address

  Philipp Hoschka
  W3C/ERCIM
  2004, route des Lucioles - B.P. 93
  06902 Sophia Antipolis Cedex
  FRANCE

  EMail: [email protected]















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Full Copyright Statement

  Copyright (C) The Internet Society (2006).

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  contained in BCP 78, and except as set forth therein, the authors
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Acknowledgement

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