Licensed under CC0 (https://creativecommons.org/publicdomain/zero/1.0/deed)

twitch-speakout.js

window.addEventListener('message', function(e) {
  const data = e.data || {};
  if (data.type !== 'item')
    return;
  const message = data.message || {};
  const obj = { detail: { command: message.command, body: message.body, from: message.from }};
  
  const synth = window.speechSynthesis;
  if (obj.detail.command === 'PRIVMSG') {
    var utter = new SpeechSynthesisUtterance(obj.detail.body);
    utter.voice = synth.getVoices().filter(v => v.lang === 'ja-JP')[0];
    utter.rate = 1;
    utter.pitch = 1;
    synth.speak(utter);
  }
});

@yuichitanakadesu Sorry for the very late reply. I got some reports that recent OBS seems to read comments by itself (i.e., the browser inside OBS can use speech API), I haven't confirmed yet though. In this case, you won't need the external browser anymore so please just close it.