wavewave/lib/wav_packer.js

Record and stream WAV audio data in the browser across all platforms

/**
 * Raw wav audio file contents
 * @typedef {Object} WavPackerAudioType
 * @property {Blob} blob
 * @property {string} url
 * @property {number} channelCount
 * @property {number} sampleRate
 * @property {number} duration
 */

/**
 * Utility class for assembling PCM16 "audio/wav" data
 * @class
 */
export class WavPacker {
  /**
   * Converts Float32Array of amplitude data to ArrayBuffer in Int16Array format
   * @param {Float32Array} float32Array
   * @returns {ArrayBuffer}
   */
  static floatTo16BitPCM(float32Array) {
    const buffer = new ArrayBuffer(float32Array.length * 2)
    const view = new DataView(buffer)
    let offset = 0
    for (let i = 0; i < float32Array.length; i++, offset += 2) {
      let s = Math.max(-1, Math.min(1, float32Array[i]))
      view.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7fff, true)
    }
    return buffer
  }

  /**
   * Concatenates two ArrayBuffers
   * @param {ArrayBuffer} leftBuffer
   * @param {ArrayBuffer} rightBuffer
   * @returns {ArrayBuffer}
   */
  static mergeBuffers(leftBuffer, rightBuffer) {
    const tmpArray = new Uint8Array(
      leftBuffer.byteLength + rightBuffer.byteLength,
    )
    tmpArray.set(new Uint8Array(leftBuffer), 0)
    tmpArray.set(new Uint8Array(rightBuffer), leftBuffer.byteLength)
    return tmpArray.buffer
  }

  /**
   * Packs data into an Int16 format
   * @private
   * @param {number} size 0 = 1x Int16, 1 = 2x Int16
   * @param {number} arg value to pack
   * @returns
   */
  _packData(size, arg) {
    return [
      new Uint8Array([arg, arg >> 8]),
      new Uint8Array([arg, arg >> 8, arg >> 16, arg >> 24]),
    ][size]
  }

  /**
   * Packs audio into "audio/wav" Blob
   * @param {number} sampleRate
   * @param {{bitsPerSample: number, channels: Array<Float32Array>, data: Int16Array}} audio
   * @returns {WavPackerAudioType}
   */
  pack(sampleRate, audio) {
    if (!audio?.bitsPerSample) {
      throw new Error(`Missing "bitsPerSample"`)
    } else if (!audio?.channels) {
      throw new Error(`Missing "channels"`)
    } else if (!audio?.data) {
      throw new Error(`Missing "data"`)
    }
    const { bitsPerSample, channels, data } = audio
    const output = [
      // Header
      "RIFF",
      this._packData(
        1,
        4 + (8 + 24) /* chunk 1 length */ + (8 + 8) /* chunk 2 length */,
      ), // Length
      "WAVE",
      // chunk 1
      "fmt ", // Sub-chunk identifier
      this._packData(1, 16), // Chunk length
      this._packData(0, 1), // Audio format (1 is linear quantization)
      this._packData(0, channels.length),
      this._packData(1, sampleRate),
      this._packData(1, (sampleRate * channels.length * bitsPerSample) / 8), // Byte rate
      this._packData(0, (channels.length * bitsPerSample) / 8),
      this._packData(0, bitsPerSample),
      // chunk 2
      "data", // Sub-chunk identifier
      this._packData(
        1,
        (channels[0].length * channels.length * bitsPerSample) / 8,
      ), // Chunk length
      data,
    ]
    const blob = new Blob(output, { type: "audio/mpeg" })
    const url = URL.createObjectURL(blob)
    return {
      blob,
      url,
      channelCount: channels.length,
      sampleRate,
      duration: data.byteLength / (channels.length * sampleRate * 2),
    }
  }
}

globalThis.WavPacker = WavPacker