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rfc:rfc4536

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.

Hoschka Informational [Page 1] RFC 4536 application/smil and application/smil+xml May 2006

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

Hoschka Informational [Page 2] RFC 4536 application/smil and application/smil+xml May 2006

 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.

Hoschka Informational [Page 3] RFC 4536 application/smil and application/smil+xml May 2006

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.

Hoschka Informational [Page 4] RFC 4536 application/smil and application/smil+xml May 2006

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.

Hoschka Informational [Page 5] RFC 4536 application/smil and application/smil+xml May 2006

 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.

Hoschka Informational [Page 6] RFC 4536 application/smil and application/smil+xml May 2006

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: ph@w3.org

Hoschka Informational [Page 7] RFC 4536 application/smil and application/smil+xml May 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Hoschka Informational [Page 8]

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