recognizer-processor.js

class RecognizerAudioProcessor extends AudioWorkletProcessor {
  constructor(options) {
    super(options);
    
    this.port.onmessage = this._processMessage.bind(this);
  }
  
  _processMessage(event) {
    console.debug(`Received event ${JSON.stringify(event.data, null, 2)}`);
    if (event.data.action === "init") {
      this._recognizerId = event.data.recognizerId;
      this._recognizerPort = event.ports[0];
    }
  }
  
  process(inputs, outputs, parameters) {
    const data = inputs[0][0];
    if (this._recognizerPort && data) {
      // AudioBuffer samples are represented as floating point numbers between -1.0 and 1.0 whilst
      // Kaldi expects them to be between -32768 and 32767 (the range of a signed int16)
      const audioArray = data.map((value) => value * 0x8000);
    
      this._recognizerPort.postMessage(
        {
          action: "audioChunk",
          data: audioArray,
          recognizerId: this._recognizerId,
          sampleRate, // Part of AudioWorkletGlobalScope
        },
        {
          transfer: [audioArray.buffer],
        }
      );
    }
    return true;
  }
}

registerProcessor('recognizer-processor', RecognizerAudioProcessor)