chatwoot/app/javascript/dashboard/components/widgets/WootWriter/utils/mp3ConversionUtils.js

import lamejs from '@breezystack/lamejs';

const writeString = (view, offset, string) => {
  // eslint-disable-next-line no-plusplus
  for (let i = 0; i < string.length; i++) {
    view.setUint8(offset + i, string.charCodeAt(i));
  }
};

const bufferToWav = async (buffer, numChannels, sampleRate) => {
  const length = buffer.length * numChannels * 2;
  const wav = new ArrayBuffer(44 + length);
  const view = new DataView(wav);

  // WAV Header
  writeString(view, 0, 'RIFF');
  view.setUint32(4, 36 + length, true);
  writeString(view, 8, 'WAVE');
  writeString(view, 12, 'fmt ');
  view.setUint32(16, 16, true);
  view.setUint16(20, 1, true);
  view.setUint16(22, numChannels, true);
  view.setUint32(24, sampleRate, true);
  view.setUint32(28, sampleRate * numChannels * 2, true);
  view.setUint16(32, numChannels * 2, true);
  view.setUint16(34, 16, true);
  writeString(view, 36, 'data');
  view.setUint32(40, length, true);

  // WAV Data
  const offset = 44;
  // eslint-disable-next-line no-plusplus
  for (let i = 0; i < buffer.length; i++) {
    // eslint-disable-next-line no-plusplus
    for (let channel = 0; channel < numChannels; channel++) {
      const sample = Math.max(
        -1,
        Math.min(1, buffer.getChannelData(channel)[i])
      );
      view.setInt16(
        offset + (i * numChannels + channel) * 2,
        sample * 0x7fff,
        true
      );
    }
  }

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

const decodeAudioData = async audioBlob => {
  const audioContext = new (window.AudioContext || window.webkitAudioContext)();
  const arrayBuffer = await audioBlob.arrayBuffer();
  const audioData = await audioContext.decodeAudioData(arrayBuffer);
  return audioData;
};

export const convertToWav = async audioBlob => {
  const audioBuffer = await decodeAudioData(audioBlob);
  return bufferToWav(
    audioBuffer,
    audioBuffer.numberOfChannels,
    audioBuffer.sampleRate
  );
};

/**
 * Encodes audio samples to MP3 format.
 * @param {number} channels - Number of audio channels.
 * @param {number} sampleRate - Sample rate in Hz.
 * @param {Int16Array} samples - Audio samples to be encoded.
 * @param {number} bitrate - MP3 bitrate (default: 128)
 * @returns {Blob} - The MP3 encoded audio as a Blob.
 */
export const encodeToMP3 = (channels, sampleRate, samples, bitrate = 128) => {
  const outputBuffer = [];
  const encoder = new lamejs.Mp3Encoder(channels, sampleRate, bitrate);
  const maxSamplesPerFrame = 1152;

  for (let offset = 0; offset < samples.length; offset += maxSamplesPerFrame) {
    const sliceEnd = Math.min(offset + maxSamplesPerFrame, samples.length);
    const sampleSlice = samples.subarray(offset, sliceEnd);
    const mp3Buffer = encoder.encodeBuffer(sampleSlice);

    if (mp3Buffer.length > 0) {
      outputBuffer.push(new Int8Array(mp3Buffer));
    }
  }

  const remainingData = encoder.flush();
  if (remainingData.length > 0) {
    outputBuffer.push(new Int8Array(remainingData));
  }

  return new Blob(outputBuffer, { type: 'audio/mp3' });
};

/**
 * Converts an audio Blob to an MP3 format Blob.
 * @param {Blob} audioBlob - The audio data as a Blob.
 * @param {number} bitrate - MP3 bitrate (default: 128)
 * @returns {Promise<Blob>} - A Blob containing the MP3 encoded audio.
 */
export const convertToMp3 = async (audioBlob, bitrate = 128) => {
  try {
    const audioBuffer = await decodeAudioData(audioBlob);
    const samples = new Int16Array(
      audioBuffer.length * audioBuffer.numberOfChannels
    );
    let offset = 0;
    for (let i = 0; i < audioBuffer.length; i += 1) {
      for (
        let channel = 0;
        channel < audioBuffer.numberOfChannels;
        channel += 1
      ) {
        const sample = Math.max(
          -1,
          Math.min(1, audioBuffer.getChannelData(channel)[i])
        );
        samples[offset] = sample < 0 ? sample * 0x8000 : sample * 0x7fff;
        offset += 1;
      }
    }
    return encodeToMP3(
      audioBuffer.numberOfChannels,
      audioBuffer.sampleRate,
      samples,
      bitrate
    );
  } catch (error) {
    throw new Error('Conversion to MP3 failed.');
  }
};

export const convertAudio = async (inputBlob, outputFormat, bitrate = 128) => {
  let audio;
  if (outputFormat === 'audio/wav') {
    audio = await convertToWav(inputBlob);
  } else if (outputFormat === 'audio/mp3') {
    audio = await convertToMp3(inputBlob, bitrate);
  } else {
    throw new Error('Unsupported output format');
  }
  return audio;
};