Content Duration MIME Header Definition
A one-line mail header that states how many seconds a voice or video attachment lasts.
Vaudreuil, G. and G. Parsons, "Content Duration MIME Header Definition", RFC 3803, DOI 10.17487/RFC3803, June 2004, <https://www.rfc-editor.org/info/rfc3803>.
@misc{rfc3803,
series = {Request for Comments},
number = 3803,
howpublished = {RFC 3803},
publisher = {RFC Editor},
doi = {10.17487/RFC3803},
url = {https://www.rfc-editor.org/info/rfc3803},
author = {G. Vaudreuil and G. Parsons},
title = {{Content Duration MIME Header Definition}},
pagetotal = 5,
year = 2004,
month = jun,
} RFC text
Contents
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.
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.
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
[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.
6. Changes from RFC 2424
Only editorial and boilerplate changes from RFC 2424 have been made
to this document.
7. Authors' Addresses
Gregory M. Vaudreuil
Lucent Technologies
7291 Williamson Rd
Dallas, TX 75214
United States
EMail: gregv@ieee.org
Glenn W. Parsons
Nortel Networks
P.O. Box 3511, Station C
Ottawa, ON K1Y 4H7
Canada
Phone: +1-613-763-7582
Fax: +1-613-763-2697
EMail: gparsons@nortelnetworks.com
8. Full Copyright Statement
Copyright (C) The Internet Society (2004). 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
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
AI ELI5
On this page
§1What the Header Is For
Time-varying media such as a spoken voice message or a video clip has an inherent duration. Many encodings store it internally or let you work it out from the byte length. Even so, it can be useful to put the duration in a MIME header so it is available without dealing with the content.
This document defines the Content-Duration header for any such content, typically audio/* or video/*. It obsoletes RFC 2424, and the only differences are editorial and boilerplate changes.
Instead of playing a song to learn how long it is, you read the number written on the case.
§2Syntax and Meaning
The value is a single number of seconds, with no units tag. The formal rule is duration := "Content-Duration" ":" 1*10DIGIT. In practice the upper bound is 2147483647, which is 2^31 - 1. An example is Content-Duration: 33, meaning 33 seconds.
The time value should be exact, but the exact figure cannot be known without playing the content. If an exact value is needed, playing it is the method to use. The header just lets a sender put a value in an easy place. How a receiver shows it, for example in the inbox or when the attachment is opened, is a local implementation issue.
The number is a plain count of seconds, like 33. It is the sender's best answer, not a stopwatch reading.
§3Use in Voice Mail
The header is a useful part of the Voice Profile for Internet Mail version 2 (VPIM), defined in RFC 3801. All VPIM messages MUST contain the audio/32KADPCM sub-type to carry the audio of a voice message. Showing the duration helps, for instance, on a simple MIME or non-MIME desktop where opening the audio is awkward.
Voice mail systems use it so you can see how long a message is before listening.
§4Security Considerations
Putting the duration outside the binary data may be a security issue in some environments, though likely not most, and in those it should not be noted. The header cannot be trusted to determine the exact size of the data. The exact length must be found by examining the data itself.
Do not believe the label when it matters. Check the real recording.