withWaveHeader.js

export const concatArrayBuffers = (buffer1: ArrayBuffer, buffer2: Buffer) => {
  const tmp = new Uint8Array(buffer1.byteLength + buffer2.byteLength);

  tmp.set(new Uint8Array(buffer1), 0);
  tmp.set(new Uint8Array(buffer2), buffer1.byteLength);

  return tmp.buffer;
};

export const withWaveHeader = (data: Buffer, numberOfChannels: number, sampleRate: number) => {
  const header = new ArrayBuffer(44);
  const view = new DataView(header);
  let pos = 0;

  function setUint16(data: any) {
    view.setUint16(pos, data, true);
    pos += 2;
  }

  function setUint32(data: any) {
    view.setUint32(pos, data, true);
    pos += 4;
  }

  // write WAVE header
  setUint32(0x46464952); // "RIFF"
  setUint32(length - 8); // file length - 8
  setUint32(0x45564157); // "WAVE"
  setUint32(0x20746d66); // "fmt " chunk
  setUint32(16); // length = 16

  setUint16(1); // PCM (uncompressed)
  setUint16(numberOfChannels);
  setUint32(sampleRate);
  setUint32(sampleRate * 2 * numberOfChannels); // avg. bytes/sec
  setUint16(numberOfChannels * 2); // block-align
  setUint16(16); // 16-bit (hardcoded in this demo)

  setUint32(0x61746164); // "data" - chunk
  setUint32(length - pos - 4); // chunk length

  return concatArrayBuffers(header, data);
};