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MPEG_audio_spatial

Contributors

  • ISO/IEC SC29 WG3 (MPEG Systems) - Scene Description Breakout Group
  • Contacts

Status

Based on ISO/IEC FDIS 23090-14

Dependencies

Written against the glTF 2.0 spec.

Overview

The MPEG_audio_spatial extension adds support for spatial audio and it may be included at top level or attached to any node in the scene.

The MPEG_audio_spatial extension supports three different node types:

  • source: an audio source that provides input audio data into the scene. Mono object and HOA sources are supported in this version of the document.
    • Type: Object or HOA
    • HOA audio sources shall ignore the parent node's position and be rendered only in 3DoF.
  • reverb: A reverb effect can be attached to the output of an audio source. Several reverb units can exist and sound sources can feed into one or more of these reverb units. An audio renderer that does not support reverb shall ignore it if the bypass attribute is set to true. If the bypass attribute is set to false, the audio renderer shall return an error message
  • listener: An audio listener represents the output of audio in the scene. A listener should be attached to a camera node in the scene. By being a child node of the camera, additional transformations can be applied to the audio listener relative to the transformation applied to the parent camera.

glTF Schema Updates

MPEG_audio_spatial Properties

Type Description Required
sources MPEG_audio_spatial.source [1-*] An array of audio sources. No
listener MPEG_audio_spatial.listener No
reverbs MPEG_audio_spatial.reverb [1-*] An array of reverb items No
extensions object JSON object with extension-specific objects. No
extras any Application-specific data. No

Additional properties are allowed.

MPEG_audio_spatial.sources

An array of audio sources.

MPEG_audio_spatial.listener

MPEG_audio_spatial.reverbs

An array of reverb items

MPEG_audio_spatial.extensions

JSON object with extension-specific objects.

  • Type: object
  • Required: No
  • Type of each property: Extension

MPEG_audio_spatial.extras

Application-specific data.

  • Type: any
  • Required: No

MPEG_audio_spatial.listener

MPEG_audio_spatial.listener Properties

Type Description Required
id integer A unique identifier ✓ Yes
extensions object JSON object with extension-specific objects. No
extras any Application-specific data. No

Additional properties are allowed.

MPEG_audio_spatial.listener.id

A unique identifier of the audio listener in the scene.

  • Type: integer
  • Required: ✓ Yes

MPEG_audio_spatial.listener.extensions

JSON object with extension-specific objects.

  • Type: object
  • Required: No
  • Type of each property: Extension

MPEG_audio_spatial.listener.extras

Application-specific data.

  • Type: any
  • Required: No

MPEG_audio_spatial.reverb

MPEG_audio_spatial.reverb Properties

Type Description Required
id any A unique identifier ✓ Yes
bypass boolean Indicates if the reverb unit can be bypassed if the audio renderer does not support it. No, default: true
properties MPEG_audio_spatial.reverb.property [1-*] An array of property items ✓ Yes
predelay number Delay of audio source. No, default: 0
extensions object JSON object with extension-specific objects. No
extras any Application-specific data. No

Additional properties are allowed.

MPEG_audio_spatial.reverb.id

A unique identifier of the audio reverb unit in the scene.

  • Type: any
  • Required: ✓ Yes

MPEG_audio_spatial.reverb.bypass

Indicates if the reverb unit can be bypassed if the audio renderer does not support it.

  • Type: boolean
  • Required: No, default: true

MPEG_audio_spatial.reverb.properties

Array of items that contains reverb property objects describing reverb unit specific parameters

MPEG_audio_spatial.reverb.predelay

Delay in seconds from onset of source to onset of late reverberation for which DSR is provided.

  • Type: number
  • Required: No, default: 0

MPEG_audio_spatial.reverb.extensions

JSON object with extension-specific objects.

  • Type: object
  • Required: No
  • Type of each property: Extension

MPEG_audio_spatial.reverb.extras

Application-specific data.

  • Type: any
  • Required: No

MPEG_audio_spatial.reverb.property

MPEG_audio_spatial.reverb.property Properties

Type Description Required
frequency number Frequency for RT60 and DSR values ✓ Yes
RT60 number Specifies RT60 value in seconds for the frequency provided in the frequency field ✓ Yes
DSR number Specifies Diffuse-to-Source Ratio value in dB for the frequency provided in the frequency field. ✓ Yes
extensions object JSON object with extension-specific objects. No
extras any Application-specific data. No

Additional properties are allowed.

MPEG_audio_spatial.reverb.property.frequency

Frequency for the provided RT60 and DSR values.

  • Type: number
  • Required: ✓ Yes

MPEG_audio_spatial.reverb.property.RT60

Specifies RT60 value in seconds for the frequency provided in the frequency field

  • Type: number
  • Required: ✓ Yes

MPEG_audio_spatial.reverb.property.DSR

Specifies Diffuse-to-Source Ratio value in dB for the frequency provided in the frequency field. For details see ISO/IEC 23090-14:5.4.1.4.

  • Type: number
  • Required: ✓ Yes

MPEG_audio_spatial.reverb.property.extensions

JSON object with extension-specific objects.

  • Type: object
  • Required: No
  • Type of each property: Extension

MPEG_audio_spatial.reverb.property.extras

Application-specific data.

  • Type: any
  • Required: No

MPEG_audio_spatial.source

MPEG_audio_spatial.source Properties

Type Description Required
id integer A unique identifier ✓ Yes
type string A type of the audio source ✓ Yes
pregain number A level-adjustment of the audio source No, default: 0
playbackSpeed number Playback speed of the audio source No, default: 1
attenuation any A function used to calculate the attenuation of the audio source. No, default: linearDistance
attenuationParameters number [1-*] An array of attenuation parameters No
referenceDistance number A distance in meters. No, default: 1
accessors integer [1-*] An array of accessors that describe the audio source ✓ Yes
reverbFeed integer [] An array of pointers to reverb units No
reverbFeedGain number [] An array of gain values No
extensions object JSON object with extension-specific objects. No
extras any Application-specific data. No

Additional properties are allowed.

MPEG_audio_spatial.source.id

A unique identifier of the audio source in the scene.

  • Type: integer
  • Required: ✓ Yes

MPEG_audio_spatial.source.type

Indicates the type of the audio source. type value equal to Object indicates mono object. type value equal to HOA indicates HOA object

  • Type: string
  • Required: ✓ Yes
  • Allowed values:
    • "Object"
    • "HOA"

MPEG_audio_spatial.source.pregain

Provides a level-adjustment in dB for the signal associated with the source.

  • Type: number
  • Required: No, default: 0
  • Minimum: >= 0

MPEG_audio_spatial.source.playbackSpeed

Playback speed of the audio signal. A value of 1.0 corresponds to playback at normal speed. The value shall be between 0.5 and 2.0.

  • Type: number
  • Required: No, default: 1
  • Minimum: >= 0.5
  • Maximum: <= 2

MPEG_audio_spatial.source.attenuation

Indicates the function used to calculate the attenuation of the audio signal based on the distance to the source. attenuation value equal to noAttenuation indicates no attenuation function should be used. attenuation value equal to inverseDistance indicates inverse distance function should be used. attenuation value equal to linearDistance indicates linear distance function should be used. attenuation value equal to exponentialDistance indicates exponential distance function should be used. attenuation value equal to custom indicates custom function should be used. The definition of custom function is outside of the scope of ISO/IEC 23090-14. The attenuation functions and their parameters are defined in ISO/IEC 23090-14:Annex D.

  • Type: any
  • Required: No, default: linearDistance
  • Allowed values:
    • noAttenuation
    • inverseDistance
    • linearDistance
    • exponentialDistance
    • custom

MPEG_audio_spatial.source.attenuationParameters

An array of parameters that are input to the attenuation function. The semantics of these parameters depend on the attenuation function itself and are defined in ISO/IEC 23090-14

  • Type: number [1-*]
  • Required: No

MPEG_audio_spatial.source.referenceDistance

Provides the distance in meters for which the distance gain is implicitly included in the source signal after application of pregain. When type equals ‘HOA’ the element shall not be present.

  • Type: number
  • Required: No, default: 1
  • Minimum: >= 1

MPEG_audio_spatial.source.accessors

An array of accessor references, by specifying the accessors indices in `accessors array, that describe the buffers where the decoded audio will be made available.

  • Type: integer [1-*]
    • Each element in the array MUST be greater than or equal to 0.
  • Required: ✓ Yes

MPEG_audio_spatial.source.reverbFeed

Provides one or more pointers to reverb units, optionally extended by a floating point scaling factor. A reverb unit represents a reverberation audio processor that is configured by the metadata from a single reverb object. Typically, a reverb object represents reverberation properties of a single room.

  • Type: integer []
  • Required: No

MPEG_audio_spatial.source.reverbFeedGain

Provides an array of gain [dB] values to be applied to the source’s signal(s) when feeding it to the corresponding reverbFeed. The array shall have the same number of elements as the reverbFeed array field.

  • Type: number []
  • Required: No

MPEG_audio_spatial.source.extensions

JSON object with extension-specific objects.

  • Type: object
  • Required: No
  • Type of each property: Extension

MPEG_audio_spatial.source.extras

Application-specific data.

  • Type: any
  • Required: No

Interaction with other extensions

The MPEG_audio_spatial works with the MPEG_accessor_timed to reference audio sources.

Known Implementations

Resources

  • ISO/IEC FDIS 23090-14, Information technology — Coded representation of immersive media — Part 14: Scene Description
  • ISO/IEC WD 23090-24, Information technology — Coded representation of immersive media — Part 24: Conformance and Reference Software for Scene Description for MPEG Media

License

Copyright ISO/IEC 2022

The use of the "MPEG scene description extensions" is subject to the license as accessible here: https://standards.iso.org/ and is subject to the IPR policy as accessible here: https://www.iso.org/iso-standards-and-patents.html.