Audio/Video Transport Group B. Wimmer, B. Hammer Internet Draft Siemens AG Document: March 2000 Category: Informational MIME Type Registration of AMR Speech Codec 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 This document defines MIME-name audio/AMR, encoding format definitions and its parameters for GSM Adaptive Multi Rate (AMR) speech codec for storage purpose. 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. Introduction GSM Adaptive Multi Rate (AMR) codec [3] is a speech codec developed by the European Telecommunications Standards Institute (ETSI). The AMR codec is the mandatory speech codec for GSM and for third generation systems by 3GPP. Although the AMR-codec was primarily designed for wireless systems it gives excellent speech quality also for wirelined systems. Wimmer & Hammer Internet Draft September 2000 [Page 1] Internet Draft MIME Type Registration of AMR Speech Codec March 2000 The AMR allows eight different speech coding modes. The bit-rates range from 4.75 to 12.2 kbit/s, see Table 1. The sampling rate is 8000 Hz and processing is performed on 20 ms frames. Coding mode bit-rate note -------------------------------------------- 0 4.75 kbit/s 1 5.15 kbit/s 2 5.9 kbit/s 3 6.7 kbit/s PDC-EFR 4 7.4 kbit/s IS-641 [5] 5 7.95 kbit/s 6 10.2 kbit/s 7 12.2 kbit/s GSM EFR [6] Table 1: AMR speech coding modes As noted in Table 1 several rates are equivalent to other standards. Standard-compliant implementations [3] must support all eight coding modes. In addition to this, mode change may occur at any time. Furthermore Discontinuous Transmission / comfort noise (DTX/CN) functionality [7] may be used. Besides [7] for the particular coding modes 3, 4 and 7 specific DTX/CN schemes are defined, see [5][6][8]. For storing AMR frames e.g. as a file or attachment, the AMR frames must be formatted according to [9]. Because no exchange of particular coding parameters, e.g. specific DTX/CN mode, can be signaled before downloading or receiving the AMR file or attachment, therefore the receiving entity (AMR decoder) must be able to decode all eight coding modes as well as the AMR DTX/CN [7]. All other DTX/CNs are not mandatory. 4. MIME Registration MIME-name for the AMR codec is allocated from IETF tree since AMR is expected to be the widely used speech codec in wireless and wirelined Internet messaging and email applications. This MIME type shall be used for stored AMR data only, e.g. attachment in an email message. It may be also used by the 3G Multimedia Messaging Service (MMS) [8]. Media Type name: audio Media subtype name: AMR Required parameters: none Optional parameters: none Encoding considerations: Each audio frame must be formatted in octet format according to [9]. The audio frames must be organized in sequential order. This implies that the first octet after frame n must be the first octet of frame (n+1). Each receiving entity that Wimmer & Hammer Internet Draft September 2000 [Page 2] Internet Draft MIME Type Registration of AMR Speech Codec March 2000 accepts this MIME type must be able to decode all eight AMR coding modes [3] and the AMR DTX/CN [7]. Security considerations: none Interoperability considerations: none Public specification: please refer to chapter 5 "references". Additional information: Magic number: none File extensions: amr, AMR Macintosh file type code: none Object identifier or OID: none Personal information Bernhard Wimmer, Siemens AG Bernard Hammer, Siemens AG E-Mail: bernhard.wimmer@mch.siemens.de, bernard.hammer@icn.siemens.de Intended usage: COMMON. It is expected that many Internet applications (as well as mobile applications) will use this type. Author/Change controller: bernhard.wimmer@mch.siemens.de 5. References [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 [3] GSM 06.90: Adaptive Multi-Rate (AMR) Speech Transcoding [4] RCR STD-27H, Personal Digital Cellular Telecommunication System RCR Standard [5] TIA/EIA -136-Rev.A, part 410 - TDMA Cellular/PCS - Radio Interface, Enhanced Full Rate Voice Codec (ACELP). Formerly IS-641. TIA published standard, 1998 [6] GSM 06.60: Enhanced Full Rate (EFR) Speech Transcoding [7] GSM 06.92: Comfort noise aspects for Adaptive Multi-Rate (AMR) speech traffic channels Wimmer & Hammer Internet Draft September 2000 [Page 3] Internet Draft MIME Type Registration of AMR Speech Codec March 2000 [8] 3G TS 23.140, "Multimedia Messaging Service (MMS)", Functional Description [9] 3G TS 26.101 (V.3.0.0) - Mandatory Speech Codec Speech Processing Functions, AMR Speech Codec Frame Structure 5. Contact Person Bernhard Wimmer Siemens AG Grillparzer Street 12A 81675 Muenchen Germany Phone: +49-89-722-23247 Email: bernhard.wimmer@mch.siemens.de Bernard Hammer Siemens AG Hofmann Street 51 81000 Muenchen Germany Phone: - Email: bernard.hammer@icn.siemens.de 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 Wimmer & Hammer Internet Draft September 2000 [Page 4]