Network Working Group                                   Greg Vaudreuil
    Internet Draft                                    Octel Communications
    Expires in six months                                    Glenn Parsons
                                                         Nortel Technology
                                                             July 29, 1997
                                Content Duration
                             MIME Header Definition
      Status of this Memo
      This document is an Internet Draft.  Internet Drafts are working
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      Directories on (Africa), (Europe), (Pacific Rim), (US East Coast), or (US West Coast).
      This document describes the MIME header Content-Duration that is
      intended for use with any timed media content (typically audio/* or
    Internet Draft             Content-Duration              July 29, 1997
      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.
      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
      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
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    Internet Draft             Content-Duration              July 29, 1997
      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.
      4. Security considerations:
      This defintion 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
      5. Authors' Addresses
      Glenn W. Parsons
      Nortel Technology
      P.O. Box 3511, Station C
      Ottawa, ON  K1Y 4H7
      Phone: +1-613-763-7582
      Fax: +1-613-763-8385
      Gregory M. Vaudreuil
      Octel Communications
      17080 Dallas Parkway
      Dallas, TX  75248-1905
      United States
      Phone/Fax: +1-972-733-2722
      6. References
      [MIME2] N. Freed and N. Borenstein,  "Multipurpose Internet Mail
           Extensions (MIME) Part Two: Media Types ", RFC 2046, Innosoft,
           First Virtual, Nov 1996.
      [VPIM2] Greg Vaudreuil and Glenn Parsons, "Voice Profile for
           Internet Mail - version 2", Work in Progress, <draft-ema-vpim-
           06.txt> July 1997.
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