create-silent-audio/index.js

Generate a silent audio blob

function createSilentAudio (time, freq = 44100){
  const length = time * freq;
  const AudioContext = window.AudioContext || window.webkitAudioContext || window.mozAudioContext;
  if(! AudioContext ){
    console.log("No Audio Context")
  }
  const context = new AudioContext();
  const audioFile = context.createBuffer(1, length, freq);
  return URL.createObjectURL(bufferToWave(audioFile, length));
}

function bufferToWave(abuffer, len) {
  let numOfChan = abuffer.numberOfChannels,
    length = len * numOfChan * 2 + 44,
    buffer = new ArrayBuffer(length),
    view = new DataView(buffer),
    channels = [], i, sample,
    offset = 0,
    pos = 0;

  // write WAVE header
  setUint32(0x46464952);
  setUint32(length - 8);
  setUint32(0x45564157);

  setUint32(0x20746d66);
  setUint32(16);
  setUint16(1);
  setUint16(numOfChan);
  setUint32(abuffer.sampleRate);
  setUint32(abuffer.sampleRate * 2 * numOfChan);
  setUint16(numOfChan * 2);
  setUint16(16);

  setUint32(0x61746164);
  setUint32(length - pos - 4);

  // write interleaved data
  for(i = 0; i < abuffer.numberOfChannels; i++)
    channels.push(abuffer.getChannelData(i));

  while(pos < length) {
    for(i = 0; i < numOfChan; i++) {             // interleave channels
      sample = Math.max(-1, Math.min(1, channels[i][offset])); // clamp
      sample = (0.5 + sample < 0 ? sample * 32768 : sample * 32767)|0; // scale to 16-bit signed int
      view.setInt16(pos, sample, true);          // write 16-bit sample
      pos += 2;
    }
    offset++                                     // next source sample
  }

  // create Blob
  return new Blob([buffer], {type: "audio/wav"});

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

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

module.exports = { createSilentAudio };