Ambisonics in an Ogg Opus Container
draft-ietf-codec-ambisonics-10

[Ballot comment]
Thanks for everyone's work on this document. I have two minor comments.

---------------------------------------------------------------------------

§4:

Are implementors intended to assume that the elided matrix coefficients are all
0.0? If so, it's probably best to say so explicitly.

---------------------------------------------------------------------------

§6:

To be clear, these code points that are being reserved are for experimental
channel mappings in general, not just channel mappings that are specific to
ambisonics, right? If so, I would suggest calling this out explicitly.

[Ballot comment]
I see that Section 5.2 attempts to Update RFC 7845 to allow for the larger
channel mapping information used by family 3, but I'm still a little
unclear about what behavior I should expect from a pure RFC 7845
implementation that receives a family 3 stream.  The actual mapping table
would be "too long", but would the implementation detect that, or just note
that it's an unrecognized family and generate silence?

Section 1

I think we want to say "by adding itesm with values 2 and 3" to the
registry, since we add two entries and not a single superposed entry.

Section 3.1

While I can deduce this from the list of allowed numbers of channels,
noting that both ends of the range (0 and 14) are allowed values probably
would add clarity.
 
Section 3.2

Figure 3 could perhaps make it more clear that C and K are not necessarily
equal.

The term "side information" is used without definition (and is not used in
RFC 7845).  Does this clause really add anything in comparison to if we
just say "The matrix MUST be provided in the channel mapping table portion
of the identification header, in place of a normal channel mapping table"?

Section 5.1

Family 255 is specified in Section 5.1.1.3 of RFC 7845, not 5.1.1.4.
(Also, the unqualified Section references should probably all be of the
form Section N of RFC 7845, for the benefift of the HTML linkification
tooling.)

Section 8

Sometimes I see a "Description" column that allows for in-registry
visibility that a range is for experimental usage.  I suppose it would not
be too hard to also modify the registry structure to add such a thing, if
you want.

[Ballot comment]
Rich version of this review at:
https://mozphab-ietf.devsvcdev.mozaws.net/D3213



IMPORTANT
S 3.2.
>                                                        | Stream Count  |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        | Coupled Count | Demixing Matrix                              :
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 
>          Figure 4: Channel Mapping Table for Channel Mapping Family 3

Are you saying I MUST use family 3?


S 5.2.
>        The remaining channel mapping families (2...254) are reserved.  A
>        demuxer implementation encountering a 'channel mapping family'
>        value that it does not recognize SHOULD NOT attempt to decode the
>        packets and SHOULD NOT use any information except for the first 19
>        octets of the ID header packet (Fig. 2) and the comment header
>        (Fig. 10).

What is the rationale for this change? Also, why are you doing it in
this document? This seems like it's going to be extremely hard for
implementors to find in future.

This is outside the DISCUSS criteria, but I would strongly recommend
you split this into a separate document.


COMMENTS
S 3.2.
>      whether or not there is a separate non-diegetic stereo stream.  This
>      corresponds to periphonic ambisonics from zeroth to fourteenth order
>      plus potentially two channels of non-diegetic stereo.  Explicitly the
>      allowed number of channels are 1, 3, 4, 6, 9, 11, 16, 18, 25, 27, 36,
>      38, 49, 51, 64, 66, 81, 83, 100, 102, 121, 123, 144, 146, 169, 171,
>      196, 198, 225, and 227.

This seems like the same graf as in 3.1, so perhaps merge these?


S 3.2.
> 
>                Figure 3: Demixing in Channel Mapping Family 3
> 
>      The matrix MUST be provided as side information and MUST be stored in
>      the channel mapping table part of the identification header, c.f.
>      section 5.1.1 in [RFC7845].  The matrix replaces the need for a

I don't think you want "c.f." here, b/c "cf." means "compare". I
suspect you just want "see". Also, there's no period between c and f.


S 5.1.
>      Figure 6: Stereo Downmixing Matrix for Channel Mapping Family 2 and 3
>            - Ambisonic Channels Plus a Non-diegetic Stereo Stream
> 
>  5.  Updates to RFC 7845
> 
>  5.1.  Format of the Channel Mapping Table

What are the interop implications of this? I.e., is a file formatted
according to this document at all playable with an existing Ogg
decoder? If not, perhaps say so

[Ballot comment]
Rich version of this review at:
https://mozphab-ietf.devsvcdev.mozaws.net/D3213



IMPORTANT
S 3.2.
>                                                        | Stream Count  |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        | Coupled Count | Demixing Matrix                              :
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 
>          Figure 4: Channel Mapping Table for Channel Mapping Family 3

Are you saying I MUST use family 3?


S 5.2.
>        The remaining channel mapping families (2...254) are reserved.  A
>        demuxer implementation encountering a 'channel mapping family'
>        value that it does not recognize SHOULD NOT attempt to decode the
>        packets and SHOULD NOT use any information except for the first 19
>        octets of the ID header packet (Fig. 2) and the comment header
>        (Fig. 10).

What is the rationale for this change? Also, why are you doing it in
this document? This seems like it's going to be extremely hard for
implementors to find in future.

COMMENTS
S 3.2.
>      whether or not there is a separate non-diegetic stereo stream.  This
>      corresponds to periphonic ambisonics from zeroth to fourteenth order
>      plus potentially two channels of non-diegetic stereo.  Explicitly the
>      allowed number of channels are 1, 3, 4, 6, 9, 11, 16, 18, 25, 27, 36,
>      38, 49, 51, 64, 66, 81, 83, 100, 102, 121, 123, 144, 146, 169, 171,
>      196, 198, 225, and 227.

This seems like the same graf as in 3.1, so perhaps merge these?


S 3.2.
> 
>                Figure 3: Demixing in Channel Mapping Family 3
> 
>      The matrix MUST be provided as side information and MUST be stored in
>      the channel mapping table part of the identification header, c.f.
>      section 5.1.1 in [RFC7845].  The matrix replaces the need for a

I don't think you want "c.f." here, b/c "cf." means "compare". I
suspect you just want "see". Also, there's no period between c and f.


S 5.1.
>      Figure 6: Stereo Downmixing Matrix for Channel Mapping Family 2 and 3
>            - Ambisonic Channels Plus a Non-diegetic Stereo Stream
> 
>  5.  Updates to RFC 7845
> 
>  5.1.  Format of the Channel Mapping Table

What are the interop implications of this? I.e., is a file formatted
according to this document at all playable with an existing Ogg
decoder? If not, perhaps say so

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

The IANA Functions Operator has completed its review of draft-ietf-codec-ambisonics-07. If any part of this review is inaccurate, please let us know.

The IANA Functions Operator understands that, upon approval of this document, there is a single action which we must complete.

First, in the Opus Channel Mapping Families registry located at:

https://www.iana.org/assignments/opus-channel-mapping-families/

the registry is updated with the following three, new values:

Value: 2
Reference: [ RFC-to-be; section 3.1 ]

Value: 3
Reference: [ RFC-to-be; section 3.2 ]

Value: 240-254
Reference: [ RFC-to-be; section 6 ]

As this document requests registrations in a Specification Required (see RFC 8126) registry, we will initiate the required Expert Review via a separate request. If there is no expert designated for the registry, we will work with the IESG to have one assigned. Expert review will need to be completed before your document can be approved for publication as an RFC.

The IANA Functions Operator understands that this is the only action required to be completed upon approval of this document.

Note:  The actions requested in this document will not be completed until the document has been approved for publication as an RFC. This message is meant only to confirm the list of actions that will be performed.

Thank you,

Sabrina Tanamal
Senior IANA Services Specialist

The following Last Call announcement was sent out (ends 2018-07-10):

From: The IESG
To: IETF-Announce
CC: ben@nostrum.com, draft-ietf-codec-ambisonics@ietf.org, codec@ietf.org, tterriberry@mozilla.com, Tim Terriberry , codec-chairs@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Ambisonics in an Ogg Opus Container) to Proposed Standard


The IESG has received a request from the Internet Wideband Audio Codec WG
(codec) to consider the following document: - 'Ambisonics in an Ogg Opus
Container'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits final
comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2018-07-10. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the beginning of
the Subject line to allow automated sorting.

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.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-codec-ambisonics/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-codec-ambisonics/ballot/

The following IPR Declarations may be related to this I-D:

  https://datatracker.ietf.org/ipr/3200/

This is my AD Evaluation of draft-ietf-codec-ambisonics-06. Overall the draft is in good shape. I just have a couple of minor comments/questions, and a few editorial comments.
————————————————

*** Substantive ***:

§3.2, last sentence: "
Also note that the total output channel number, C, MUST be set in the 3rd field of the identification header.”

Is that MUST intended as a new normative requirement? The wording makes it seem more like a statement of fact. (The prefix of “Also note that…” tends to suggest the sentence is an FYI rather than a normative requirement.

§4: I am a little confused by the MAYs in this section. Are there other alternatives? Is this an example approach? A sentence or two of context would be helpful.

*** Editorial ***:

§2: Please use the boilerplate from RFC 8174 unless there is a reason to do otherwise. (I note at least one lower case normative keyword (“should”); there may be more.

§3.1,

- first paragraph: First sentence is a fragment. Should there be a conjunction between the last two values in the list of allowed numbers of channels? (The pattern repeats in §3.2)

- figure 1: It would be helpful to define “order” and “degree” (defined in figure 2) prior to using them.

§5.2, first sentence: Missing article before “Treatment”.

§7: s/ “need take” / “need to take"

As required by RFC 4858, this is the current template for the Document
Shepherd Write-Up.

Changes are expected over time. This version is dated 24 February 2012.

(1) What type of RFC is being requested (BCP, Proposed Standard,
Internet Standard, Informational, Experimental, or Historic)?  Why
is this the proper type of RFC?  Is this type of RFC indicated in the
title page header?

Proposed Standard. This is the proper type of RFC as this document adds normative requirements for implementations that wish to support ambisonics in the Ogg Opus format described by RFC 7845, and also updates RFC 7845 (if approved).

(2) The IESG approval announcement includes a Document Announcement
Write-Up. Please provide such a Document Announcement Write-Up. Recent
examples can be found in the "Action" announcements for approved
documents. The approval announcement contains the following sections:

Technical Summary

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.

Working Group Summary

There were no particularly controversial aspects of this draft, and consensus on all decisions was generally easy to reach.

Document Quality

The format has been implemented in the open-source libopus library (using an experimental mapping family identifier), with support included in the opus-tools package. Several significant vendors have indicated a plan to implement the specification, including Gooogle, Mozilla, and the open source VideoLAN and FFmpeg projects. Mark Harris performed a particularly thorough review, and motivated many of the necessary updates to RFC 7845. In addition, the updates to the "Opus Channel Mapping Families" IANA registry were reviewed by the original authors of RFC 7845 (which created that registry).

Personnel

  Who is the Document Shepherd? Who is the Responsible Area
  Director?

Document Shepherd: Timothy B. Terriberry
Responsible Area Director: Ben Campbell

(3) Briefly describe the review of this document that was performed by
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for publication, please explain why the document is being forwarded to
the IESG.

I have been involved with this document since it was first brought to the IETF, and even originally recommended to the authors that the work be brought here. I have reviewed all of the revisions in detail, and as an author of the original RFC 7845 and a developer of the libopus open-source project, I believe that the proposed format is technically sound and explained in sufficient detail to enable other implementations. I believe this document is ready for publication.

(4) Does the document Shepherd have any concerns about the depth or
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No.

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This document has no AAA, DNS, DCHP, XML, or internationalization components, and I believe that it raises no new security or operation complexity issues beyond those of RFC 7845. Therefore we have not sought such review.

(6) Describe any specific concerns or issues that the Document Shepherd
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I have received confirmation from Jan Skoglund. Michael Graczyk has left Google, who was employing him to work on this draft, and I have been unsuccessful in contacting him. However, Jan Skoglund was his boss at Google and believes that any and all appropriate IPR disclosures have already been filed.

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If so, summarize any WG discussion and conclusion regarding the IPR
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The following IPR disclosure has been filed:
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There has been no discussion on the mailing list. Since the application has been offered with Royalty-Free, Reasonable and Non-Discriminatory terms, and only relates to one specific aspect of one possible method for encoding, we do not anticipate any issues.

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