Add WAV support

src/lib/mp3-encoder.js

@@ -0,0 +1,49 @@
+import { Mp3Encoder } from 'lamejs'
+
+export default class {
+  constructor(config) {
+    this.bitRate    = config.bitRate
+    this.sampleRate = config.sampleRate
+    this.dataBuffer = []
+    this.encoder    = new Mp3Encoder(1, this.sampleRate, this.bitRate)
+  }
+
+  encode(arrayBuffer) {
+    const maxSamples = 1152
+    const samples    = this._convertBuffer(arrayBuffer)
+    let remaining    = samples.length
+
+    for (let i = 0; remaining >= 0; i += maxSamples) {
+      const left = samples.subarray(i, i + maxSamples)
+      const buffer = this.encoder.encodeBuffer(left)
+      this.dataBuffer.push(new Int8Array(buffer))
+      remaining -= maxSamples
+    }
+  }
+
+  finish() {
+    this.dataBuffer.push(this.encoder.flush())
+    const blob = new Blob(this.dataBuffer, { type: 'audio/mp3' })
+    this.dataBuffer = []
+
+    return {
+      id   : Date.now(),
+      blob : blob,
+      url  : URL.createObjectURL(blob)
+    }
+  }
+
+  _floatTo16BitPCM(input, output) {
+    for (let i = 0; i < input.length; i++) {
+      const s = Math.max(-1, Math.min(1, input[i]))
+      output[i] = (s < 0 ? s * 0x8000 : s * 0x7FFF)
+    }
+  }
+
+  _convertBuffer(arrayBuffer) {
+    const data = new Float32Array(arrayBuffer)
+    const out = new Int16Array(arrayBuffer.length)
+    this._floatTo16BitPCM(data, out)
+    return out
+  }
+}