Ambisonics in an Ogg Opus Container Agenda Ambisonics Foundations - - PowerPoint PPT Presentation

▶
ambisonics in an ogg opus container agenda
SMART_READER_LITE
LIVE PREVIEW

Ambisonics in an Ogg Opus Container Agenda Ambisonics Foundations - - PowerPoint PPT Presentation

May 27, 2023 32 likes •284 views

Ambisonics in an Ogg Opus Container Agenda Ambisonics Foundations Adding Ambisonics to Opus Mappings Calculations Opus function calls Agenda Ambisonics Foundations Adding Ambisonics to Opus Mappings

slide-1
SLIDE 1

Ambisonics in an Ogg Opus Container

slide-2
SLIDE 2

Agenda

  • Ambisonics Foundations
  • Adding Ambisonics to Opus
  • Mappings
  • Calculations
  • Opus function calls
slide-3
SLIDE 3

Agenda

  • Ambisonics Foundations
  • Adding Ambisonics to Opus
  • Mappings
  • Calculations
  • Opus function calls
slide-4
SLIDE 4
slide-5
SLIDE 5
slide-6
SLIDE 6
slide-7
SLIDE 7
slide-8
SLIDE 8
slide-9
SLIDE 9

First order Approximation

slide-10
SLIDE 10

= + + +

slide-11
SLIDE 11
slide-12
SLIDE 12

1st order 4 channels 3rd order 16 channels Reality

slide-13
SLIDE 13
slide-14
SLIDE 14

Chrome

slide-15
SLIDE 15

Agenda

  • Ambisonics Foundations
  • Adding Ambisonics to Opus
  • Mappings
  • Calculations
  • Opus function calls
slide-16
SLIDE 16

Channel Mappings

  • Ambisonics Opus Channel Mapping 2 & 3
  • A demuxer implementation encountering Channel

Mapping Family 2 or Family 3 MUST interpret the Opus stream as containing ambisonics

slide-17
SLIDE 17

General Channel Mapping for 2 & 3

  • Allowed numbers of channels:

(1 + n)2 + 2j

for n = 0...14 and j = 0 or 1 n denotes the ambisonic order j denotes separate non-diegetic (non-head-tracked) stereo stream

  • Channels can be zeroed-out to support ‘mixed-order’

ambisonics

slide-18
SLIDE 18

Channel Mapping 2 & 3 Representation

  • Order of Ambisonics Channel Number (ACN)

ACN = n * (n + 1) + m for order n and degree m; followed by 2 optional channels of non-diegetic stereo indexed (L, R)

  • Ambisonic channels are expected to be normalized with

Schmidt Semi-Normalization (SN3D)

slide-19
SLIDE 19

Coding Details Channel Mapping 2

  • Variable bit rate allocation
  • More bits in the ‘W’

(Omnidirectional) Channel

slide-20
SLIDE 20

Coding Details Channel Mapping 3

decoder encoder

KEY U = encoder input streams X = encoded/decoded channels, S = decoder output streams C = num. of input/output channels K = num. of streams + num. of coupled streams A = mixing matrix D = demixing matrix (stored in header)

slide-21
SLIDE 21

Channel Mapping Tables

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+ | Stream Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Coupled Count | Demixing Matrix : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Channel Mapping Family 3’s Mapping Table

  • Mapping 2 uses Mapping 1’s Mapping Table
slide-22
SLIDE 22

Proposed Opus API Changes Encoding & Decoding Channel Mapping 2

OpusMSEncoder *opus_multistream_surround_encoder_create(..., mapping_family = 2, ...); OpusMSDecoder *opus_multistream_surround_decoder_create(...);

slide-23
SLIDE 23

Proposed Opus API Changes Encoding & Decoding Channel Mapping 3

OpusAmbEncoder *opus_ambisonics_surround_encoder_create(..., mapping_family = 3, (out)MappingMatrix *demixing_matrix);

  • r

OpusAmbEncoder *opus_ambisonics_encoder_create(..., mapping_family = 3, (in)MappingMatrix *mixing_matrix); OpusAmbDecoder *opus_ambisonics_decoder_create(..., (in)MappingMatrix *demixing_matrix);

slide-24
SLIDE 24

Questions

slide-25
SLIDE 25

Comparison of Results

VisQol @ 192kbps Vorbis Opus Opus 4:3 Vorbis Opus Opus 4:3 VisQol @ 128kbps Opus 128kbps Opus 4:3 128kbps Opus 192kbps Opus 4:3 192kbps Directivity