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/*).
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].
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
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.
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.
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
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.
[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.
[DUR] Parsons, G. and G. Vaudreuil, "Content Duration MIME Header
Definition", RFC 2424, September 1998.
[VPIM2] Vaudreuil, G. and G. Parsons, "Voice Profile for Internet
Mail - version 2", RFC 2421, September 1998.
Only editorial and boilerplate changes from RFC 2424 have been made
to this document.
Vaudreuil, et al. Standards Track [Page 3]
RFC 3803 Content Duration MIME Header Definition June 2004
Copyright (C) The Internet Society (2004). This document is subject
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Vaudreuil, et al. Standards Track [Page 5]