Ambisonics in an Ogg Opus Container
RFC 8486

Document Type RFC - Proposed Standard (October 2018; No errata)
Updates RFC 7845
Last updated 2018-10-29
Replaces draft-graczyk-codec-ambisonics
Stream IETF
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Stream WG state Submitted to IESG for Publication
Document shepherd Tim Terriberry
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Send notices to Tim Terriberry <tterriberry@mozilla.com>
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Internet Engineering Task Force (IETF)                       J. Skoglund
Request for Comments: 8486                                    Google LLC
Updates: 7845                                                 M. Graczyk
Category: Standards Track                                   October 2018
ISSN: 2070-1721

                  Ambisonics in an Ogg Opus Container

Abstract

   This document defines an extension to the Opus audio codec to
   encapsulate coded Ambisonics using the Ogg format.  It also contains
   updates to RFC 7845 to reflect necessary changes in the description
   of channel mapping families.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8486.

Copyright Notice

   Copyright (c) 2018 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
   (https://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.

Skoglund & Graczyk           Standards Track                    [Page 1]
RFC 8486                     Opus Ambisonics                October 2018

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Ambisonics with Ogg Opus  . . . . . . . . . . . . . . . . . .   3
     3.1.  Channel Mapping Family 2  . . . . . . . . . . . . . . . .   3
     3.2.  Channel Mapping Family 3  . . . . . . . . . . . . . . . .   4
     3.3.  Allowed Numbers of Channels . . . . . . . . . . . . . . .   5
   4.  Downmixing  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Updates to RFC 7845 . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Format of the Channel Mapping Table . . . . . . . . . . .   7
     5.2.  Unknown Mapping Families  . . . . . . . . . . . . . . . .   8
   6.  Experimental Mapping Families . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Ambisonics is a representation format for three-dimensional sound
   fields that can be used for surround sound and immersive virtual-
   reality playback.  See [fellgett75] and [daniel04] for technical
   details on the Ambisonics format.  For the purposes of the this
   document, Ambisonics can be considered a multichannel audio stream.
   A separate stereo stream can be used alongside the Ambisonics in a
   head-tracked virtual reality experience to provide so-called non-
   diegetic audio -- that is, audio that should remain unchanged by
   rotation of the listener's head, such as narration or stereo music.
   Ogg is a general-purpose container, supporting audio, video, and
   other media.  It can be used to encapsulate audio streams coded using
   the Opus codec.  See [RFC6716] and [RFC7845] for technical details on
   the Opus codec and its encapsulation in the Ogg container,
   respectively.

   This document extends the Ogg Opus format by defining two new channel
   mapping families for encoding Ambisonics.  The Ogg Opus format is
   extended indirectly by adding items with values 2 and 3 to the "Opus
   Channel Mapping Families" IANA registry.  When 2 or 3 are used as the
   Channel Mapping Family Number in an Ogg stream, the semantic meaning
   of the channels in the multichannel Opus stream is one of the
   Ambisonics layouts defined in this document.  This mapping can also
   be used in other contexts that make use of the channel mappings
   defined by the "Opus Channel Mapping Families" registry.

Skoglund & Graczyk           Standards Track                    [Page 2]
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