jambonz-api-server/lib/record/encoder.js

const { Transform } = require('stream');
const lamejs = require('@jambonz/lamejs');

class PCMToMP3Encoder extends Transform {
  constructor(options) {
    super(options);

    const channels = options.channels || 1;
    const sampleRate = options.sampleRate || 8000;
    const bitRate = options.bitRate || 128;

    this.encoder = new lamejs.Mp3Encoder(channels, sampleRate, bitRate);
    this.channels = channels;
  }

  _transform(chunk, encoding, callback) {
    // Convert chunk buffer into Int16Array for lamejs
    const samples = new Int16Array(chunk.buffer, chunk.byteOffset, chunk.length / 2);

    // Split input samples into left and right channel arrays if stereo
    let leftChannel, rightChannel;
    if (this.channels === 2) {
      leftChannel = new Int16Array(samples.length / 2);
      rightChannel = new Int16Array(samples.length / 2);

      for (let i = 0; i < samples.length; i += 2) {
        leftChannel[i / 2] = samples[i];
        rightChannel[i / 2] = samples[i + 1];
      }
    } else {
      leftChannel = samples;
    }

    // Encode the input data
    const mp3Data = this.encoder.encodeBuffer(leftChannel, rightChannel);

    if (mp3Data.length > 0) {
      this.push(Buffer.from(mp3Data));
    }
    callback();
  }

  _flush(callback) {
    // Finalize encoding and flush the internal buffers
    const mp3Data = this.encoder.flush();

    if (mp3Data.length > 0) {
      this.push(Buffer.from(mp3Data));
    }
    callback();
  }
}

module.exports = PCMToMP3Encoder;