Content Duration MIME Header Definition
RFC 3803

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Network Working Group                                       G. Vaudreuil
Request for Comments: 3803                           Lucent Technologies
Obsoletes: 2424                                               G. Parsons
Category: Standards Track                                Nortel Networks
                                                               June 2004

                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 (2004).

Abstract

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

1.  Introduction

   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.  This document obsoletes RFC 2424.

   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 RFC 2119 [REQ].

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.

Vaudreuil, et al.           Standards Track                     [Page 1]
RFC 3803        Content Duration MIME Header Definition        June 2004

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.

Vaudreuil, et al.           Standards Track                     [Page 2]
RFC 3803        Content Duration MIME Header Definition        June 2004

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.  References

5.1.  Normative References

   [MIME2]   Gellens, R., "The Text/Plain Format Parameter", RFC 2646,
             August 1999.

   [VPIM2R2] Vaudreuil, G., and G. Parsons, "Voice Profile for Internet
             Mail - version 2 (VPIMv2)", RFC 3801, June 2004.

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

5.2.  Informative References