Network Working Group G. Vaudreuil Request for Comments: 3803 Lucent Technologies Obsoletes: 2424 G. Parsons Category: Standards Track Nortel Networks June 2004Content Duration MIME Header Definition
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.
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.
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RFC 3803 Content Duration MIME Header Definition June 2004 2.1. SyntaxThe Content-Duration field's value is a single number specifying the time duration in seconds of the content. Formally:
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.
2.3. Example
In this example the content duration represents 33 seconds:
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.
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RFC 3803 Content Duration MIME Header Definition June 2004 4. Security ConsiderationsThis 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,
5.2. Informative References
[DUR] Parsons, G. and G. Vaudreuil, "Content Duration MIME Header
6. Changes from RFC 2424
Only editorial and boilerplate changes from RFC 2424 have been made to this document.
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RFC 3803 Content Duration MIME Header Definition June 2004 7. Authors' AddressesGregory M. Vaudreuil Lucent Technologies 7291 Williamson Rd Dallas, TX 75214 United States
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RFC 3803 Content Duration MIME Header Definition June 2004 8. Full Copyright StatementCopyright (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.
