Updates to the Opus Audio Codec
draft-ietf-codec-opus-update-07

The information below is for an old version of the document
Document Type Active Internet-Draft (codec WG)
Last updated 2017-07-25 (latest revision 2017-07-16)
Replaces draft-valin-codec-opus-update
Stream IETF
Intended RFC status Proposed Standard
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Stream WG state Submitted to IESG for Publication
Document shepherd Tim Terriberry
Shepherd write-up Show (last changed 2017-07-21)
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Send notices to Tim Terriberry <tterriberry@mozilla.com>
Network Working Group                                          JM. Valin
Internet-Draft                                       Mozilla Corporation
Updates: 6716 (if approved)                                       K. Vos
Intended status: Standards Track                                 vocTone
Expires: January 17, 2018                                  July 16, 2017

                    Updates to the Opus Audio Codec
                    draft-ietf-codec-opus-update-07

Abstract

   This document addresses minor issues that were found in the
   specification of the Opus audio codec in RFC 6716.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 17, 2018.

Copyright Notice

   Copyright (c) 2017 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
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   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.

Valin & Vos             Expires January 17, 2018                [Page 1]
Internet-Draft                 Opus Update                     July 2017

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Stereo State Reset in SILK  . . . . . . . . . . . . . . . . .   3
   4.  Parsing of the Opus Packet Padding  . . . . . . . . . . . . .   3
   5.  Resampler buffer  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Integer wrap-around in inverse gain computation . . . . . . .   6
   7.  Integer wrap-around in LSF decoding . . . . . . . . . . . . .   6
   8.  Cap on Band Energy  . . . . . . . . . . . . . . . . . . . . .   7
   9.  Hybrid Folding  . . . . . . . . . . . . . . . . . . . . . . .   7
   10. Downmix to Mono . . . . . . . . . . . . . . . . . . . . . . .   9
   11. New Test Vectors  . . . . . . . . . . . . . . . . . . . . . .   9
   12. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   15. Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   This document addresses minor issues that were discovered in the
   reference implementation of the Opus codec that serves as the
   specification in RFC 6716 [RFC6716].  Only issues affecting the
   decoder are listed here.  An up-to-date implementation of the Opus
   encoder can be found at <https://opus-codec.org/>.

   Some of the changes in this document update normative behaviour in a
   way that requires new test vectors.  The English text of the
   specification is unaffected, only the C implementation is.  The
   updated specification remains fully compatible with the original
   specification.

   Note: due to RFC formatting conventions, lines exceeding the column
   width in the patch are split using a backslash character.  The
   backslashes at the end of a line and the white space at the beginning
   of the following line are not part of the patch.  A properly
   formatted patch including all changes is available at
   <https://www.ietf.org/proceedings/98/slides/materials-98-codec-opus-
   update-00.patch>.

2.  Terminology

   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 [RFC2119].

Valin & Vos             Expires January 17, 2018                [Page 2]
Internet-Draft                 Opus Update                     July 2017

3.  Stereo State Reset in SILK

   The reference implementation does not reinitialize the stereo state
   during a mode switch.  The old stereo memory can produce a brief
   impulse (i.e. single sample) in the decoded audio.  This can be fixed
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