Offline feature extraction in Meyda v2

meyda-v2-offline.js

//Because meyda v2 doesn't really have an offline extraction API, we need to manually require some stuff
var jsfft = require("./node_modules/meyda/node_modules/jsfft/")
var complex_array = require("./node_modules/meyda/node_modules/jsfft/lib/complex_array.js")
var extractors = require("./node_modules/meyda/dist/node/featureExtractors.js")
var meyda_utils = require("meyda").utils
//this is a simple class for streaming WAV data as Float32Arrays
//available at https://gist.github.com/jakubfiala/cb9de100fdd4f043d46e
//we're not going to use its streaming functionality for simplicity
var WavManager = require("./wav-manager.js")
var fs = require('fs')

//extraction parameters
var bufSize = 1024
var hopSize = 512

//this is the core of the hack - we circumvent the SPN inside Meyda by calculating the spectrum ourselves (using jsfft)
//so we can pass it to the extractor function directly
function getSpectrum(_d) {

	var windowedSignal = meyda_utils.applyWindow(_d, 'hanning')
	// create complexarray to hold the spectrum
	var data = new complex_array.ComplexArray(_d.length)
	// map time domain
	data.map(function(value, i, n) {
		value.real = windowedSignal[i]
	})
	// transform
	var spec = data.FFT()
	// assign to meyda
	var ampSpectrum = new Float32Array(_d.length/2)
	for (var i = 0; i < _d.length/2; i++) {
		ampSpectrum[i] = Math.sqrt(Math.pow(spec.real[i],2) + Math.pow(spec.imag[i],2))
	}

	return ampSpectrum
}

var mfccs = []

//the constructor of WavManager takes 2 functions as args
//one to handle the stream chunk by chunk,
//and one to handle the full final data
// it's not very elegant or efficient, but whatever
var wm = new WavManager(function(data){},
	function(fulldata){
		//callback for stream end

		//we iterate through the data frame by frame
		for (var i = 0; i < fulldata.length-bufSize; i += hopSize) {
			//get the chunk
			var chunk = fulldata.subarray(i, i+bufSize)

			//call the extractor function and pass in the spectrum of the chunk
			mfccs.push(extractors.mfcc({
				ampSpectrum: getSpectrum(chunk),
				bufferSize: bufSize,
				sampleRate: 44100 //change this if needed
			}))

		}
	}
)

console.log("results:", mfccs)

HELPPPPPPPPPPPPP!!!!!!!