Add existing code

src/lib/wav-encoder.js

@@ -0,0 +1,59 @@
+export default class {
+  constructor (options) {
+    this.bufferSize = options.bufferSize || 4096
+    this.sampleRate = options.sampleRate
+    this.samples    = options.samples
+  }
+
+  getData () {
+    this._joinSamples()
+
+    let buffer = new ArrayBuffer(44 + this.samples.length * 2)
+    let view   = new DataView(buffer)
+
+    this._writeString(view, 0, 'RIFF')                       // RIFF identifier
+    view.setUint32(4, 36 + this.samples.length * 2, true)    // RIFF chunk length
+    this._writeString(view, 8, 'WAVE')                       // RIFF type
+    this._writeString(view, 12, 'fmt ')                      // format chunk identifier
+    view.setUint32(16, 16, true)                             // format chunk length
+    view.setUint16(20, 1, true)                              // sample format (raw)
+    view.setUint16(22, 1, true)                              // channel count
+    view.setUint32(24, this.sampleRate, true)                // sample rate
+    view.setUint32(28, this.sampleRate * 4, true)            // byte rate (sample rate * block align)
+    view.setUint16(32, 4, true)                              // block align (channel count * bytes per sample)
+    view.setUint16(34, 16, true)                             // bits per sample
+    this._writeString(view, 36, 'data')                      // data chunk identifier
+    view.setUint32(40, this.samples.length * 2, true)        // data chunk length
+
+    this._floatTo16BitPCM(view, 44, this.samples)
+
+    return new Blob([view], {type: 'audio/wav'})
+  }
+
+  _floatTo16BitPCM (output, offset, input) {
+    for (let i = 0; i < input.length; i++, offset += 2) {
+      let s = Math.max(-1, Math.min(1, input[i]))
+      output.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7FFF, true)
+    }
+  }
+
+  _joinSamples () {
+    let recordLength  = this.samples.length * this.bufferSize
+    let joinedSamples = new Float64Array(recordLength)
+    let offset        = 0
+
+    for (let i = 0; i < this.samples.length; i++) {
+      let sample = this.samples[i]
+      joinedSamples.set(sample, offset)
+      offset += sample.length
+    }
+
+    this.samples = joinedSamples
+  }
+
+  _writeString (view, offset, string) {
+    for (let i = 0; i < string.length; i++) {
+      view.setUint8(offset + i, string.charCodeAt(i))
+    }
+  }
+}