Internet Engineering Task Force J. Flaks Internet Draft Dolby Laboratories Document: draft-flaks-audio-ac3-00.txt October Category: Audio MIME type The audio/ac3 Media Type Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 1. Abstract In recent years we have begun to see a convergence of Internet technologies with traditional media formats such as video and audio. It is therefore likely that movies and television with surround sound capabilities are soon to be dispersed around the Internet. AC-3 is standard multi-channel compression format for HDTV, DVD, and other video formats, but there is no uniform MIME type for these files. 2. Conventions used in this document 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 [2]. 3. AC-3 Audio The audio compression method defined as AC-3 as described in ATSC- Digital Audio Compression Standard [4] is a popular method of compressing multi-channel audio while maintaining high fidelity. The audio/ac3 Media Type October 2000 An AC-3 frame contains 1536 samples of compressed data, as well as other bit stream information. Data rates vary from 32 kbps to 640 kbps. The audio data is compressed by using a psychoacoustic model to determine what data is inaudible to the human ear. Then unnecessary data is removed from the bit stream. 4. MIME Types MIME media type name: audio MIME subtype name: ac3 Required parameters: none Optional parameters: none Encoding considerations: AC-3 audio data is binary data. Base 64 encoding is suitable for Email. Security considerations: None known at the time of writing Interoperability considerations: None known at the time of writing Published specification: See [4] Applications: Multi-channel audio encoding Additional information: Magic number(s): None File extension(s): .ac3 Macintosh File Type Code(s): None Object Identifier(s) or OID(s): None Personal information: Jason Flaks Email: jsf@dolby.com Intended usage: COMMON Author/Change controller: jsf@dolby.com 5. Formal Syntax The following syntax specification uses the augmented Backus-Naur Form (BNF) as described in RFC-2234 [3]. 6. References 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. The audio/ac3 Media Type October 2000 2 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 3 Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, Internet Mail Consortium and Demon Internet Ltd., November 1997 4 U.S. Advanced Television Systems Committee, _Digital Audio Compression (AC-3) Standard,_ Doc. A/52. Dec. 20, 1995 7. Author's Addresses Jason Flaks Dolby Labs 100 Potrero Ave San Francisco, CA 94103 Phone: (415)558-0373 Email: jsf@dolby.com The audio/ac3 Media Type October 2000 Full Copyright Statement "Copyright (C) The Internet Society (date). 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 implmentation 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