    Network Working Group                                         G. Vaudreuil
    Request for Comments: 2424                             Lucent Technologies
    Category: Standards Track                                       G. Parsons
                                                              Northern Telecom
                                                                September 1998

                                Content Duration
                             MIME Header Definition

    Status of this Memo

       This document specifies an Internet standards track protocol for the
       Internet community, and requests discussion and suggestions for
       improvements.  Please refer to the current edition of the "Internet
       Official Protocol Standards" (STD 1) for the standardization state
       and status of this protocol.  Distribution of this memo is unlimited.

    Copyright Notice

       Copyright (C) The Internet Society (1998).  All Rights Reserved.

    Overview

       This document describes the MIME header Content-Duration that is
       intended for use with any timed media content (typically audio/* or
       video/*).

    1.  Abstract

       This document describes the MIME header Content-Duration that is
       intended for use with any time varying media content (typically
       audio/* or video/*).  The length of time is represented in seconds
       without any units indication.

    2. Content-Duration Header Field

       Time varying media contents, for example, a spoken voice message or a
       video clip, have an inherent time duration.  Many audio and video
       encodings may include their duration as header information or may
       allow accurate calculation based on the byte length of the data.
       However, it may be useful to present the time duration of the content
       in a MIME header to allow its simple determination without dealing
       with the actual content.

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    RFC 2424                    Content-Duration              September 1998

       The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
       "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
       document are to be interpreted as described in [REQ].

    2.1 Syntax

       The Content-Duration field's value is a single number specifying the
       time duration in seconds of the content.  Formally:

       duration := "Content-Duration" ":" 1*10DIGIT

       Note that practically (though highly unlikely in MIME media), the
       upper bound on the numerical value of the time duration is (2^^31 -
       1) or 2147483647.

    2.2 Semantics

       This field represents the time duration of the associated time
       varying media content.  The time duration is noted in seconds with no
       units tag.  The time value should be exact, however the exact value
       of the time duration cannot be known without opening the content and
       playing it.  If an exact value must be known, then the latter method
       should be used.  This mechanism simply allows placing a sender
       determined time duration value in the header for easy access.

       Though there are several ways to present this duration to the
       recipient (e.g. with the inbox headers, when audio attachment
       opened), the actual use of this field on reception is a local
       implementation issue.

    2.3 Example

       In this example the content duration represents 33 seconds:

           Content-Duration: 33

    3. VPIM Usage

       The Content-Duration header field for the audio/32KADPCM sub-type is
       a useful component of the VPIM specification [VPIM2].  All VPIM
       Messages MUST contain this sub-type to carry the audio of a voice
       message.  It may be useful in some instances (e.g. viewing on a
       simple MIME or non-MIME desktop) to have the time duration of the
       voice message available without having to open the audio content.

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    RFC 2424                    Content-Duration              September 1998

    4. Security Considerations

       This definition introduces the option of explicitly identifying the
       time duration of an audio/* or video/* content outside of the binary
       data that forms the content.  In some environments (though likely not
       the majority), the identification of the actual time duration in a
       header field may be a security issue and as a result should not be
       noted.  Reliance on the time indicated in this header field cannot be
       trusted for the purposes of determining the exact size of the data.
       The exact length of the data must be determined by examining the data
       itself.

    5. Authors' Addresses

       Glenn W. Parsons
       Northern Telecom
       P.O. Box 3511, Station C
       Ottawa, ON  K1Y 4H7
       Canada

       Phone: +1-613-763-7582
       Fax: +1-613-763-4461
       EMail: Glenn.Parsons@Nortel.ca

       Gregory M. Vaudreuil
       Lucent Technologies
       17080 Dallas Parkway
       Dallas, TX  75248-1905
       United States

       Phone/Fax: +1-972-733-2722
       EMail: GregV@Lucent.Com

    6. References

       [MIME2] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
               Extensions (MIME) Part Two: Media Types", RFC 2046, November
               1996.

       [VPIM2] Vaudreuil, G., and G. Parsons, "Voice Profile for Internet
               Mail - version 2", RFC 2421, September 1998.

       [REQ] Bradner, S., "Key words for use in RFCs to Indicate Requirement
             Levels", BCP 14, RFC 2119, March 1997.

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    RFC 2424                    Content-Duration              September 1998

    7.  Full Copyright Statement

       Copyright (C) The Internet Society (1998).  All Rights Reserved.

       This document and translations of it may be copied and furnished to
       others, and derivative works that comment on or otherwise explain it
       or assist in its implementation may be prepared, copied, published
       and distributed, in whole or in part, without restriction of any
       kind, provided that the above copyright notice and this paragraph are
       included on all such copies and derivative works.  However, this
       document itself may not be modified in any way, such as by removing
       the copyright notice or references to the Internet Society or other
       Internet organizations, except as needed for the purpose of
       developing Internet standards in which case the procedures for
       copyrights defined in the Internet Standards process must be
       followed, or as required to translate it into languages other than
       English.

       The limited permissions granted above are perpetual and will not be
       revoked by the Internet Society or its successors or assigns.

       This document and the information contained herein is provided on an
       "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
       TASK FORCE DISCLAIMS 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 WARRANTIES OF
       MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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