generate audio file with W3C Web Speech API

Question

Is it possible to use W3C Web Speech API to write Javascript code which generates audio file (wav, ogg or mp3) with voice speaking given text? I mean, I want to do something like:

window.speechSynthesis.speak(new SpeechSynthesisUtterance("0 1 2 3"))

but I want sound generated with it not to be output to speakers but to file.

Answer 1

The requirement is not possible using Web Speech API alone, see Re: MediaStream, ArrayBuffer, Blob audio result from speak() for recording?, How to implement option to return Blob, ArrayBuffer, or AudioBuffer from window.speechSynthesis.speak() call

Though requirement is possible using a library, for example, espeak or meSpeak, see How to create or convert text to audio at chromium browser?.

fetch("https://gist.githubusercontent.com/guest271314/f48ee0658bc9b948766c67126ba9104c/raw/958dd72d317a6087df6b7297d4fee91173e0844d/mespeak.js")
  .then(response => response.text())
  .then(text => {
    const script = document.createElement("script");
    script.textContent = text;
    document.body.appendChild(script);

    return Promise.all([
      new Promise(resolve => {
        meSpeak.loadConfig("https://gist.githubusercontent.com/guest271314/8421b50dfa0e5e7e5012da132567776a/raw/501fece4fd1fbb4e73f3f0dc133b64be86dae068/mespeak_config.json", resolve)
      }),
      new Promise(resolve => {
        meSpeak.loadVoice("https://gist.githubusercontent.com/guest271314/fa0650d0e0159ac96b21beaf60766bcc/raw/82414d646a7a7ef11bb04ddffe4091f78ef121d3/en.json", resolve)
      })
    ])
  })
  .then(() => {
    // takes approximately 14 seconds to get here
    console.log(meSpeak.isConfigLoaded());
    console.log(meSpeak.speak("what it do my ninja", {
      amplitude: 100,
      pitch: 5,
      speed: 150,
      wordgap: 1,
      variant: "m7",
      rawdata: "mime"
    }));
})
.catch(err => console.log(err));

There is also workaround using MediaRecorder, depending on system hardware How to capture generated audio from window.speechSynthesis.speak() call?.