RFC2424 - Content Duration MIME Header Definition

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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.

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.

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", RFC2046, November

1996.

[VPIM2] Vaudreuil, G., and G. Parsons, "Voice Profile for Internet

Mail - version 2", RFC2421, September 1998.

[REQ] Bradner, S., "Key words for use in RFCs to Indicate Requirement

Levels", BCP 14, RFC2119, March 1997.

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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