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Definition of the Opus Audio Codec
RFC 6716

Internet Engineering Task Force (IETF)                         JM. Valin
Request for Comments: 6716                           Mozilla Corporation
Category: Standards Track                                         K. Vos
ISSN: 2070-1721                                  Skype Technologies S.A.
                                                           T. Terriberry
                                                     Mozilla Corporation
                                                          September 2012

                   Definition of the Opus Audio Codec

Abstract

   This document defines the Opus interactive speech and audio codec.
   Opus is designed to handle a wide range of interactive audio
   applications, including Voice over IP, videoconferencing, in-game
   chat, and even live, distributed music performances.  It scales from
   low bitrate narrowband speech at 6 kbit/s to very high quality stereo
   music at 510 kbit/s.  Opus uses both Linear Prediction (LP) and the
   Modified Discrete Cosine Transform (MDCT) to achieve good compression
   of both speech and music.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6716.

Valin, et al.                Standards Track                    [Page 1]
RFC 6716                 Interactive Audio Codec          September 2012

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   The licenses granted by the IETF Trust to this RFC under Section 3.c
   of the Trust Legal Provisions shall also include the right to extract
   text from Sections 1 through 8 and Appendix A and Appendix B of this
   RFC and create derivative works from these extracts, and to copy,
   publish, display and distribute such derivative works in any medium
   and for any purpose, provided that no such derivative work shall be
   presented, displayed or published in a manner that states or implies
   that it is part of this RFC or any other IETF Document.

Table of Contents

   1. Introduction ....................................................5
      1.1. Notation and Conventions ...................................6
   2. Opus Codec Overview .............................................8
      2.1. Control Parameters ........................................10
           2.1.1. Bitrate ............................................10
           2.1.2. Number of Channels (Mono/Stereo) ...................11
           2.1.3. Audio Bandwidth ....................................11
           2.1.4. Frame Duration .....................................11
           2.1.5. Complexity .........................................11
           2.1.6. Packet Loss Resilience .............................12
           2.1.7. Forward Error Correction (FEC) .....................12
           2.1.8. Constant/Variable Bitrate ..........................12
           2.1.9. Discontinuous Transmission (DTX) ...................13
   3. Internal Framing ...............................................13
      3.1. The TOC Byte ..............................................13
      3.2. Frame Packing .............................................16
           3.2.1. Frame Length Coding ................................16
           3.2.2. Code 0: One Frame in the Packet ....................16
           3.2.3. Code 1: Two Frames in the Packet, Each with
                  Equal Compressed Size ..............................17
           3.2.4. Code 2: Two Frames in the Packet, with
                  Different Compressed Sizes .........................17

Valin, et al.                Standards Track                    [Page 2]
RFC 6716                 Interactive Audio Codec          September 2012

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