rfc:rfc2424
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.
Vaudreuil & Parsons Standards Track [Page 1] RFC 2424 Content-Duration September 1998
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.
Vaudreuil & Parsons Standards Track [Page 2] RFC 2424 Content-Duration September 1998
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", RFC 2046, November
1996.
[VPIM2] Vaudreuil, G., and G. Parsons, "Voice Profile for Internet
Mail - version 2", RFC 2421, September 1998.
[REQ] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
Vaudreuil & Parsons Standards Track [Page 3] RFC 2424 Content-Duration September 1998
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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