convert audio wav to mp3 (#552)

web/app/components/base/voice-input/utils.ts

@@ -0,0 +1,38 @@
+import lamejs from 'lamejs'
+
+export const convertToMp3 = (recorder: any) => {
+  const wav = lamejs.WavHeader.readHeader(recorder.getWAV())
+  const { channels, sampleRate } = wav
+  const mp3enc = new lamejs.Mp3Encoder(channels, sampleRate, 128)
+  const result = recorder.getChannelData()
+  const buffer = []
+
+  const leftData = result.left && new Int16Array(result.left.buffer, 0, result.left.byteLength / 2)
+  const rightData = result.right && new Int16Array(result.right.buffer, 0, result.right.byteLength / 2)
+  const remaining = leftData.length + (rightData ? rightData.length : 0)
+
+  const maxSamples = 1152
+  for (let i = 0; i < remaining; i += maxSamples) {
+    const left = leftData.subarray(i, i + maxSamples)
+    let right = null
+    let mp3buf = null
+
+    if (channels === 2) {
+      right = rightData.subarray(i, i + maxSamples)
+      mp3buf = mp3enc.encodeBuffer(left, right)
+    }
+    else {
+      mp3buf = mp3enc.encodeBuffer(left)
+    }
+
+    if (mp3buf.length > 0)
+      buffer.push(mp3buf)
+  }
+
+  const enc = mp3enc.flush()
+
+  if (enc.length > 0)
+    buffer.push(enc)
+
+  return new Blob(buffer, { type: 'audio/mp3' })
+}