UsdMedia.md

UsdMedia module — pxr-usd-api 105.1 documentation

pxr-usd-api

 »
Modules »
UsdMedia module

 

# UsdMedia module

Summary: The UsdMedia module provides a representation for including other media, such as audio, in the context of a stage. UsdMedia currently contains one media type, UsdMediaSpatialAudio, which allows the playback of audio files both spatially and non-spatially.

Classes:

SpatialAudio
The SpatialAudio primitive defines basic properties for encoding playback of an audio file or stream within a USD Stage.

Tokens

class pxr.UsdMedia.SpatialAudio
The SpatialAudio primitive defines basic properties for encoding
playback of an audio file or stream within a USD Stage. The
SpatialAudio schema derives from UsdGeomXformable since it can support
full spatial audio while also supporting non-spatial mono and stereo
sounds. One or more SpatialAudio prims can be placed anywhere in the
namespace, though it is advantageous to place truly spatial audio
prims under/inside the models from which the sound emanates, so that
the audio prim need only be transformed relative to the model, rather
than copying its animation.

## Timecode Attributes and Time Scaling

startTime and endTime are timecode valued attributes which gives
them the special behavior that layer offsets affecting the layer in
which one of these values is authored are applied to the attribute’s
value itself during value resolution. This allows audio playback to be
kept in sync with time sampled animation as the animation is affected
by layer offsets in the composition. But this behavior brings with it
some interesting edge cases and caveats when it comes to layer offsets
that include scale.
Although authored layer offsets may have a time scale which can scale
the duration between an authored startTime and endTime, we make no
attempt to infer any playback dilation of the actual audio media
itself. Given that startTime and endTime can be independently
authored in different layers with differing time scales, it is not
possible, in general, to define an”original timeframe”from which we
can compute a dilation to composed stage-time. Even if we could
compute a composed dilation this way, it would still be impossible to
flatten a stage or layer stack into a single layer and still retain
the composed audio dilation using this schema.
Although we do not expect it to be common, it is possible to apply a
negative time scale to USD layers, which mostly has the effect of
reversing animation in the affected composition. If a negative scale
is applied to a composition that contains authored startTime and
endTime, it will reverse their relative ordering in time. Therefore,
we stipulate when playbackMode
is”onceFromStartToEnd”or”loopFromStartToEnd”, if endTime is less
than startTime, then begin playback at endTime, and continue until
startTime. When startTime and endTime are inverted, we do not,
however, stipulate that playback of the audio media itself be
inverted, since doing so”successfully”would require perfect knowledge
of when, within the audio clip, relevant audio ends (so that we know
how to offset the reversed audio to align it so that we reach
the”beginning”at startTime), and sounds played in reverse are not
likely to produce desirable results.
For any described attribute Fallback Value or Allowed Values
below that are text/tokens, the actual token is published and defined
in UsdMediaTokens. So to set an attribute to the value”rightHanded”,
use UsdMediaTokens->rightHanded as the value.
Methods:

CreateAuralModeAttr(defaultValue, writeSparsely)
See GetAuralModeAttr() , and also Create vs Get Property Methods for when to use Get vs Create.

CreateEndTimeAttr(defaultValue, writeSparsely)
See GetEndTimeAttr() , and also Create vs Get Property Methods for when to use Get vs Create.

CreateFilePathAttr(defaultValue, writeSparsely)
See GetFilePathAttr() , and also Create vs Get Property Methods for when to use Get vs Create.

CreateGainAttr(defaultValue, writeSparsely)
See GetGainAttr() , and also Create vs Get Property Methods for when to use Get vs Create.

CreateMediaOffsetAttr(defaultValue, ...)
See GetMediaOffsetAttr() , and also Create vs Get Property Methods for when to use Get vs Create.

CreatePlaybackModeAttr(defaultValue, ...)
See GetPlaybackModeAttr() , and also Create vs Get Property Methods for when to use Get vs Create.

CreateStartTimeAttr(defaultValue, writeSparsely)
See GetStartTimeAttr() , and also Create vs Get Property Methods for when to use Get vs Create.

Define
classmethod Define(stage, path) -> SpatialAudio

Get
classmethod Get(stage, path) -> SpatialAudio

GetAuralModeAttr()
Determines how audio should be played.

GetEndTimeAttr()
Expressed in the timeCodesPerSecond of the containing stage, endTime specifies when the audio stream will cease playing during animation playback if the length of the referenced audio clip is longer than desired.

GetFilePathAttr()
Path to the audio file.

GetGainAttr()
Multiplier on the incoming audio signal.

GetMediaOffsetAttr()
Expressed in seconds, mediaOffset specifies the offset from the referenced audio file's beginning at which we should begin playback when stage playback reaches the time that prim's audio should start.

GetPlaybackModeAttr()
Along with startTime and endTime, determines when the audio playback should start and stop during the stage's animation playback and whether the audio should loop during its duration.

GetSchemaAttributeNames
classmethod GetSchemaAttributeNames(includeInherited) -> list[TfToken]

GetStartTimeAttr()
Expressed in the timeCodesPerSecond of the containing stage, startTime specifies when the audio stream will start playing during animation playback.

CreateAuralModeAttr(defaultValue, writeSparsely) → Attribute
See GetAuralModeAttr() , and also Create vs Get Property Methods for
when to use Get vs Create.
If specified, author defaultValue as the attribute’s default,
sparsely (when it makes sense to do so) if writeSparsely is
true - the default for writeSparsely is false .

Parameters

defaultValue (VtValue) – 
writeSparsely (bool) – 

CreateEndTimeAttr(defaultValue, writeSparsely) → Attribute
See GetEndTimeAttr() , and also Create vs Get Property Methods for
when to use Get vs Create.
If specified, author defaultValue as the attribute’s default,
sparsely (when it makes sense to do so) if writeSparsely is
true - the default for writeSparsely is false .

Parameters

defaultValue (VtValue) – 
writeSparsely (bool) – 

CreateFilePathAttr(defaultValue, writeSparsely) → Attribute
See GetFilePathAttr() , and also Create vs Get Property Methods for
when to use Get vs Create.
If specified, author defaultValue as the attribute’s default,
sparsely (when it makes sense to do so) if writeSparsely is
true - the default for writeSparsely is false .

Parameters

defaultValue (VtValue) – 
writeSparsely (bool) – 

CreateGainAttr(defaultValue, writeSparsely) → Attribute
See GetGainAttr() , and also Create vs Get Property Methods for when
to use Get vs Create.
If specified, author defaultValue as the attribute’s default,
sparsely (when it makes sense to do so) if writeSparsely is
true - the default for writeSparsely is false .

Parameters

defaultValue (VtValue) – 
writeSparsely (bool) – 

CreateMediaOffsetAttr(defaultValue, writeSparsely) → Attribute
See GetMediaOffsetAttr() , and also Create vs Get Property Methods for
when to use Get vs Create.
If specified, author defaultValue as the attribute’s default,
sparsely (when it makes sense to do so) if writeSparsely is
true - the default for writeSparsely is false .

Parameters

defaultValue (VtValue) – 
writeSparsely (bool) – 

CreatePlaybackModeAttr(defaultValue, writeSparsely) → Attribute
See GetPlaybackModeAttr() , and also Create vs Get Property Methods
for when to use Get vs Create.
If specified, author defaultValue as the attribute’s default,
sparsely (when it makes sense to do so) if writeSparsely is
true - the default for writeSparsely is false .

Parameters

defaultValue (VtValue) – 
writeSparsely (bool) – 

CreateStartTimeAttr(defaultValue, writeSparsely) → Attribute
See GetStartTimeAttr() , and also Create vs Get Property Methods for
when to use Get vs Create.
If specified, author defaultValue as the attribute’s default,
sparsely (when it makes sense to do so) if writeSparsely is
true - the default for writeSparsely is false .

Parameters

defaultValue (VtValue) – 
writeSparsely (bool) – 

static Define()
classmethod Define(stage, path) -> SpatialAudio
Attempt to ensure a UsdPrim adhering to this schema at path is
defined (according to UsdPrim::IsDefined() ) on this stage.
If a prim adhering to this schema at path is already defined on
this stage, return that prim. Otherwise author an SdfPrimSpec with
specifier == SdfSpecifierDef and this schema’s prim type name for
the prim at path at the current EditTarget. Author SdfPrimSpec s
with specifier == SdfSpecifierDef and empty typeName at the
current EditTarget for any nonexistent, or existing but not Defined
ancestors.
The given path must be an absolute prim path that does not contain
any variant selections.
If it is impossible to author any of the necessary PrimSpecs, (for
example, in case path cannot map to the current UsdEditTarget ‘s
namespace) issue an error and return an invalid UsdPrim.
Note that this method may return a defined prim whose typeName does
not specify this schema class, in case a stronger typeName opinion
overrides the opinion at the current EditTarget.

Parameters

stage (Stage) – 
path (Path) – 

static Get()
classmethod Get(stage, path) -> SpatialAudio
Return a UsdMediaSpatialAudio holding the prim adhering to this schema
at path on stage .
If no prim exists at path on stage , or if the prim at that
path does not adhere to this schema, return an invalid schema object.
This is shorthand for the following:
UsdMediaSpatialAudio(stage->GetPrimAtPath(path));

Parameters

stage (Stage) – 
path (Path) – 

GetAuralModeAttr() → Attribute
Determines how audio should be played.
Valid values are:

spatial: Play the audio in 3D space if the device can support
spatial audio. if not, fall back to mono.
nonSpatial: Play the audio without regard to the SpatialAudio
prim’s position. If the audio media contains any form of stereo or
other multi-channel sound, it is left to the application to determine
whether the listener’s position should be taken into account. We
expect nonSpatial to be the choice for ambient sounds and music sound-
tracks.

Declaration
uniform token auralMode ="spatial"
C++ Type
TfToken
Usd Type
SdfValueTypeNames->Token
Variability
SdfVariabilityUniform
Allowed Values
spatial, nonSpatial

GetEndTimeAttr() → Attribute
Expressed in the timeCodesPerSecond of the containing stage, endTime
specifies when the audio stream will cease playing during animation
playback if the length of the referenced audio clip is longer than
desired.
This only applies if playbackMode is set to onceFromStartToEnd or
loopFromStartToEnd, otherwise the endTimeCode of the stage is used
instead of endTime. If endTime is less than startTime, it is
expected that the audio will instead be played from endTime to
startTime. Note that endTime is expressed as a timecode so that
the stage can properly apply layer offsets when resolving its value.
See Timecode Attributes and Time Scaling for more details and caveats.
Declaration
uniform timecode endTime = 0
C++ Type
SdfTimeCode
Usd Type
SdfValueTypeNames->TimeCode
Variability
SdfVariabilityUniform

GetFilePathAttr() → Attribute
Path to the audio file.
In general, the formats allowed for audio files is no more constrained
by USD than is image-type. As with images, however, usdz has stricter
requirements based on DMA and format support in browsers and consumer
devices. The allowed audio filetypes for usdz are M4A, MP3, WAV (in
order of preference).
Usdz Specification
Declaration
uniform asset filePath = @@
C++ Type
SdfAssetPath
Usd Type
SdfValueTypeNames->Asset
Variability
SdfVariabilityUniform

GetGainAttr() → Attribute
Multiplier on the incoming audio signal.
A value of 0”mutes”the signal. Negative values will be clamped to 0.
Declaration
double gain = 1
C++ Type
double
Usd Type
SdfValueTypeNames->Double

GetMediaOffsetAttr() → Attribute
Expressed in seconds, mediaOffset specifies the offset from the
referenced audio file’s beginning at which we should begin playback
when stage playback reaches the time that prim’s audio should start.
If the prim’s playbackMode is a looping mode, mediaOffset is
applied only to the first run-through of the audio clip; the second
and all other loops begin from the start of the audio clip.
Declaration
uniform double mediaOffset = 0
C++ Type
double
Usd Type
SdfValueTypeNames->Double
Variability
SdfVariabilityUniform

GetPlaybackModeAttr() → Attribute
Along with startTime and endTime, determines when the audio
playback should start and stop during the stage’s animation playback
and whether the audio should loop during its duration.
Valid values are:

onceFromStart: Play the audio once, starting at startTime,
continuing until the audio completes.
onceFromStartToEnd: Play the audio once beginning at startTime,
continuing until endTime or until the audio completes, whichever
comes first.
loopFromStart: Start playing the audio at startTime and
continue looping through to the stage’s authored endTimeCode.
loopFromStartToEnd: Start playing the audio at startTime and
continue looping through, stopping the audio at endTime.
loopFromStage: Start playing the audio at the stage’s authored
startTimeCode and continue looping through to the stage’s authored
endTimeCode. This can be useful for ambient sounds that should
always be active.

Declaration
uniform token playbackMode ="onceFromStart"
C++ Type
TfToken
Usd Type
SdfValueTypeNames->Token
Variability
SdfVariabilityUniform
Allowed Values
onceFromStart, onceFromStartToEnd, loopFromStart, loopFromStartToEnd,
loopFromStage

static GetSchemaAttributeNames()
classmethod GetSchemaAttributeNames(includeInherited) -> list[TfToken]
Return a vector of names of all pre-declared attributes for this
schema class and all its ancestor classes.
Does not include attributes that may be authored by custom/extended
methods of the schemas involved.

Parameters
includeInherited (bool) – 

GetStartTimeAttr() → Attribute
Expressed in the timeCodesPerSecond of the containing stage,
startTime specifies when the audio stream will start playing during
animation playback.
This value is ignored when playbackMode is set to loopFromStage as,
in this mode, the audio will always start at the stage’s authored
startTimeCode. Note that startTime is expressed as a timecode so
that the stage can properly apply layer offsets when resolving its
value. See Timecode Attributes and Time Scaling for more details and
caveats.
Declaration
uniform timecode startTime = 0
C++ Type
SdfTimeCode
Usd Type
SdfValueTypeNames->TimeCode
Variability
SdfVariabilityUniform

class pxr.UsdMedia.Tokens
Attributes:

auralMode

endTime

filePath

gain

loopFromStage

loopFromStart

loopFromStartToEnd

mediaOffset

nonSpatial

onceFromStart

onceFromStartToEnd

playbackMode

spatial

startTime

auralMode = 'auralMode'

endTime = 'endTime'

filePath = 'filePath'

gain = 'gain'

loopFromStage = 'loopFromStage'

loopFromStart = 'loopFromStart'

loopFromStartToEnd = 'loopFromStartToEnd'

mediaOffset = 'mediaOffset'

nonSpatial = 'nonSpatial'

onceFromStart = 'onceFromStart'

onceFromStartToEnd = 'onceFromStartToEnd'

playbackMode = 'playbackMode'

spatial = 'spatial'

startTime = 'startTime'

© Copyright 2019-2023, NVIDIA.
      Last updated on Nov 14, 2023.