File piper.capnp of Package sonic-visualiser
# Piper audio feature extraction: schema for low-level operation
#
# This file is formatted to 130 characters width, in order to fit the
# comments next to the schema definitions.
#
# Copyright (c) 2015-2017 Queen Mary, University of London, provided
# under a BSD-style licence. See the file COPYING for details.
@0xc4b1c6c44c999206;
using Cxx = import "/capnp/c++.capnp";
$Cxx.namespace("piper");
struct Basic {
# Basic metadata common to many Piper structures.
identifier @0 :Text; # A computer-readable string. Must match the regex /^[a-zA-Z0-9_-]+$/.
name @1 :Text; # A short human-readable name or label. Must be present.
description @2 :Text; # An optional human-readable descriptive text that may accompany the name.
}
struct ParameterDescriptor {
# Properties of an adjustable parameter. A parameter's value is just a single
# float, but the descriptor explains how to interpret and present that value.
# A Piper feature extractor has a static list of parameters. The properties of
# a given parameter never change, in contrast to output descriptors, which
# may have different properties depending on the configuration of the extractor.
basic @0 :Basic; # Basic metadata about the parameter.
unit @1 :Text; # Human-recognisable unit of the parameter (e.g. Hz). May be left empty.
minValue @2 :Float32 = 0.0; # Minimum value. Must be provided.
maxValue @3 :Float32 = 0.0; # Maximum value. Must be provided.
defaultValue @4 :Float32 = 0.0; # Default if the parameter is not set to anything else. Must be provided.
isQuantized @5 :Bool = false; # True if parameter values are quantized to a particular resolution.
quantizeStep @6 :Float32 = 0.0; # Quantization resolution, if isQuantized.
valueNames @7 :List(Text) = []; # Optional human-readable labels for the values, if isQuantized.
}
enum SampleType {
# How returned features are spaced on the input timeline.
oneSamplePerStep @0; # Each process input returns a feature aligned with that input's timestamp.
fixedSampleRate @1; # Features are equally spaced at a given sample rate.
variableSampleRate @2; # Features have their own individual timestamps.
}
struct ConfiguredOutputDescriptor {
# Properties of an output, that is, a single stream of features produced
# in response to process and finish requests. A feature extractor may
# have any number of outputs, and it always calculates and returns features
# from all of them when processing; this is useful in cases where more
# than one feature can be easily calculated using a single method.
# This structure contains the properties of an output that are not static,
# i.e. that may depend on the parameter values provided at configuration.
unit @0 :Text; # Human-recognisable unit of the bin values in output features. May be empty.
hasFixedBinCount @1 :Bool = false; # True if this output has an equal number of values in each returned feature.
binCount @2 :Int32 = 0; # Number of values per feature for this output, if hasFixedBinCount.
binNames @3 :List(Text) = []; # Optional human-readable labels for the value bins, if hasFixedBinCount.
hasKnownExtents @4 :Bool = false; # True if all feature values fall within the same fixed min/max range.
minValue @5 :Float32 = 0.0; # Minimum value in range for any value from this output, if hasKnownExtents.
maxValue @6 :Float32 = 0.0; # Maximum value in range for any value from this output, if hasKnownExtents.
isQuantized @7 :Bool = false; # True if feature values are quantized to a particular resolution.
quantizeStep @8 :Float32 = 0.0; # Quantization resolution, if isQuantized.
sampleType @9 :SampleType; # How returned features from this output are spaced on the input timeline.
sampleRate @10 :Float32 = 0.0; # Sample rate (features per second) if sampleType == fixedSampleRate.
hasDuration @11 :Bool = false; # True if features returned from this output will have a duration.
}
struct OutputDescriptor {
# All the properties of an output, both static (the basic metadata) and
# potentially dependent on configuration parameters (the configured descriptor).
basic @0 :Basic; # Basic metadata about the output.
configured @1 :ConfiguredOutputDescriptor; # Properties of the output that may depend on configuration parameters.
}
enum InputDomain {
# Whether a feature extractor requires time-domain audio input (i.e.
# "normal" or "unprocessed" audio samples) or frequency-domain input
# (i.e. resulting from windowed, usually overlapping, short-time
# Fourier transforms).
timeDomain @0; # The plugin requires time-domain audio samples as input.
frequencyDomain @1; # The plugin requires input to have been pre-processed using windowed STFTs.
}
struct ExtractorStaticData {
# Static properties of a feature extractor. That is, metadata about the
# extractor that are the same regardless of how you configure or run it.
key @0 :Text; # String that "globally" identifies the extractor, used to load it (see docs).
basic @1 :Basic; # Basic metadata about the extractor.
maker @2 :Text; # Human-readable text naming the author or vendor of the extractor.
rights @3 :Text; # Human-readable summary of copyright and/or licensing terms for the extractor.
version @4 :Int32; # Version number of extractor; must increase if new algorithm changes results.
category @5 :List(Text); # List of general->specific category labels for this extractor (see docs).
minChannelCount @6 :Int32; # Minimum number of input channels of audio this extractor can accept.
maxChannelCount @7 :Int32; # Maximum number of input channels of audio this extractor can accept.
parameters @8 :List(ParameterDescriptor); # List of configurable parameter properties for the feature extractor.
programs @9 :List(Text); # List of predefined programs. For backward-compatibility, not recommended.
inputDomain @10 :InputDomain; # Whether the extractor requires time-domain or frequency-domain input audio.
basicOutputInfo @11 :List(Basic); # Basic metadata about all of the outputs of the extractor.
}
struct RealTime {
# Time structure. When used as a timestamp, this is relative to "start
# of audio".
sec @0 :Int32 = 0; # Number of seconds.
nsec @1 :Int32 = 0; # Number of nanoseconds. Must have same sign as sec unless sec == 0.
}
struct ProcessInput {
# Audio and timing input data provided to a process request.
inputBuffers @0 :List(List(Float32)); # A single block of audio data (time or frequency domain) for each channel.
timestamp @1 :RealTime; # Time of start of block (time-domain) or "centre" of it (frequency-domain).
}
struct Feature {
# A single feature calculated and returned from a process or finish request.
hasTimestamp @0 :Bool = false; # True if feature has a timestamp. Must be true for a variableSampleRate output.
timestamp @1 :RealTime; # Timestamp of feature, if hasTimestamp.
hasDuration @2 :Bool = false; # True if feature has a duration. Must be true if output's hasDuration is true.
duration @3 :RealTime; # Duration of feature, if hasDuration.
label @4 :Text; # Optional human-readable text attached to feature.
featureValues @5 :List(Float32) = []; # The feature values themselves (of size binCount, if output hasFixedBinCount).
}
struct FeatureSet {
# The set of all features, across all outputs, calculated and returned from
# a single process or finish request.
struct FSPair {
# A mapping between output identifier and ordered list of features for
# that output.
output @0 :Text; # Output id, matching the output's descriptor's basic identifier.
features @1 :List(Feature) = []; # Features calculated for that output during the current request, in time order.
}
featurePairs @0 :List(FSPair); # The feature lists for all outputs for which any features have been calculated.
}
struct Framing {
# Determines how audio should be split up into individual buffers for input.
# If the feature extractor accepts frequency-domain input, then this
# applies prior to the STFT transform.
#
# These values are sometimes mandatory, but in other contexts one or both may
# be set to zero to mean "don't care". See documentation for structures that
# include a framing field for details.
blockSize @0 :Int32; # Number of time-domain audio samples per buffer (on each channel).
stepSize @1 :Int32; # Number of samples to advance between buffers: equals blockSize for no overlap.
}
struct Configuration {
# Bundle of parameter values and other configuration data for a feature-
# extraction procedure.
struct PVPair {
# A mapping between parameter identifier and value.
parameter @0 :Text; # Parameter id, matching the parameter's descriptor's basic identifier.
value @1 :Float32; # Value to set parameter to (within constraints given in parameter descriptor).
}
parameterValues @0 :List(PVPair); # Values for all parameters, or at least any that are to change from defaults.
currentProgram @1 :Text; # Selection of predefined program. For backward-compatibility, not recommended.
channelCount @2 :Int32; # Number of audio channels of input.
framing @3 :Framing; # Step and block size for framing the input.
}
enum AdapterFlag {
# Flags that may be used when requesting a server to load a feature
# extractor, to ask the server to do some of the work of framing and input
# conversion instead of leaving it to the client side. These affect the
# apparent behaviour of the loaded extractor.
adaptInputDomain @0; # Input-domain conversion, so the extractor always expects time-domain input.
adaptChannelCount @1; # Channel mixing or duplication, so any number of input channels is acceptable.
adaptBufferSize @2; # Framing, so the extractor accepts any blockSize of non-overlapping buffers.
}
const adaptAllSafe :List(AdapterFlag) =
[ adaptInputDomain, adaptChannelCount ];
# The set of adapter flags that can always be applied, leaving results unchanged.
const adaptAll :List(AdapterFlag) =
[ adaptInputDomain, adaptChannelCount, adaptBufferSize ];
# The set of adapter flags that may cause "equivalent" results to be returned (see documentation).
struct ListRequest {
# Request a server to provide a list of available feature extractors.
from @0 :List(Text); # If non-empty, provide only extractors found in the given list of "libraries".
}
struct ListResponse {
# Response to a successful list request.
available @0 :List(ExtractorStaticData); # List of static data about available feature extractors.
}
struct LoadRequest {
# Request a server to load a feature extractor and return a handle to it.
key @0 :Text; # Key as found in the extractor's static data structure.
inputSampleRate @1 :Float32; # Sample rate for input audio. Properties of the extractor may depend on this.
adapterFlags @2 :List(AdapterFlag); # Set of optional flags to make any framing and input conversion requests.
}
struct LoadResponse {
# Response to a successful load request.
handle @0 :Int32; # Handle to be used to refer to the loaded feature extractor in future requests.
staticData @1 :ExtractorStaticData; # Static data about this feature extractor, identical to that in list response.
defaultConfiguration @2 :Configuration; # Extractor's default parameter values and preferred input framing.
}
struct ConfigurationRequest {
# Request a server to configure a loaded feature extractor and prepare
# it for use. This request must be carried out on a feature extractor
# before any process request can be made.
handle @0 :Int32; # Handle as returned in the load response from the loading of this extractor.
configuration @1 :Configuration; # Bundle of parameter values to set, and client's preferred input framing.
}
struct ConfigurationResponse {
# Response to a successful configuration request.
handle @0 :Int32; # Handle of extractor, as passed in the configuration request.
outputs @1 :List(OutputDescriptor); # Full set of properties of all outputs following configuration.
framing @2 :Framing; # Input framing that must be used for subsequent process requests.
}
struct ProcessRequest {
# Request a server to process a buffer of audio using a loaded and
# configured feature extractor.
handle @0 :Int32; # Handle as returned in the load response from the loading of this extractor.
processInput @1 :ProcessInput; # Audio in the input domain, with framing as in the configuration response.
}
struct ProcessResponse {
# Response to a successful process request.
handle @0 :Int32; # Handle of extractor, as passed in the process request.
features @1 :FeatureSet; # All features across all outputs calculated during this process request.
}
struct FinishRequest {
# Request a server to finish processing and unload a loaded feature
# extractor. This request may be made at any time -- the extractor does
# not have to have been configured or used. The extractor handle cannot
# be used again with this server afterwards.
handle @0 :Int32; # Handle as returned in the load response from the loading of this extractor.
}
struct FinishResponse {
# Response to a successful finish request.
handle @0 :Int32; # Handle of extractor, as passed in the finish request. May not be used again.
features @1 :FeatureSet; # Features the extractor has calculated now that it knows all input has ended.
}
struct Error {
# Response to any request that fails.
code @0 :Int32; # Error code.
message @1 :Text; # Error message.
}
struct RpcRequest {
# Request bundle for use when using Cap'n Proto serialisation without
# Cap'n Proto RPC layer. For Cap'n Proto RPC, see piper.rpc.capnp.
id :union {
# Identifier used solely to associate a response packet with its
# originating request. Server does not examine the contents of this,
# it just copies the request id structure into the response.
number @0 :Int32;
tag @1 :Text;
none @2 :Void;
}
request :union {
# For more details, see the documentation for the individual
# request structures.
list @3 :ListRequest; # Provide a list of available feature extractors.
load @4 :LoadRequest; # Load a feature extractor and return a handle to it.
configure @5 :ConfigurationRequest; # Configure a loaded feature extractor, set parameters, and prepare it for use.
process @6 :ProcessRequest; # Process a single fixed-size buffer of audio and return calculated features.
finish @7 :FinishRequest; # Get any remaining features and unload the extractor.
}
}
struct RpcResponse {
# Response bundle for use when using Cap'n Proto serialisation without
# Cap'n Proto RPC layer. For Cap'n Proto RPC, see piper.rpc.capnp.
id :union {
# Identifier used solely to associate a response packet with its
# originating request. Server does not examine the contents of this,
# it just copies the request id structure into the response.
number @0 :Int32;
tag @1 :Text;
none @2 :Void;
}
response :union {
# For more details, see the documentation for the individual
# response structures.
error @3 :Error; # The request (of whatever type) failed.
list @4 :ListResponse; # List succeeded: here is static data about the requested extractors.
load @5 :LoadResponse; # Load succeeded: here is a handle for the loaded extractor.
configure @6 :ConfigurationResponse;# Configure succeeded: ready to process, here are values such as block size.
process @7 :ProcessResponse; # Process succeeded: here are all features calculated from this input block.
finish @8 :FinishResponse; # Finish succeeded: extractor unloaded, here are all remaining features.
}
}
