The Web Speech API Specification does not presently provide a means or hint on how to achieve returning or capturing and recording audio output of window.speechSynthesis.speak() call.
See also
MediaStream, ArrayBuffer, Blob audio result from speak() for recording?
Re: MediaStream, ArrayBuffer, Blob audio result from speak() for recording?
Re: MediaStream, ArrayBuffer, Blob audio result from speak() for recording?. In pertinent part, use cases include, but are not limited to
Persons who have issues speaking; i.e.g., persons whom have suffered a
stroke or other communication inhibiting afflictions. They could convert
text to an audio file and send the file to another individual or group.
This feature would go towards helping them communicate with other persons,
similar to the technologies which assist Stephen Hawking communicate;
Presently, the only person who can hear the audio output is the person
in front of the browser; in essence, not utilizing the full potential of
the text to speech functionality. The audio result can be used as an
attachment within an email; media stream; chat system; or other
communication application. That is, control over the generated audio output;
Another application would be to provide a free, libre, open source audio
dictionary and translation service - client to client and client to server,
server to client.
It is possible to capture the output of audio output of window.speechSynthesis.speak() call utilizing navigator.mediaDevices.getUserMedia() and MediaRecorder(). The expected result is returned at Chromium browser. Implementation at Firefox has issues. Select Monitor of Built-in Audio Analog Stereo at navigator.mediaDevices.getUserMedia() prompt.
The workaround is cumbersome. We should be able to get generated audio, at least as a Blob, without navigator.mediaDevices.getUserMedia() and MediaRecorder().
More interest is evidently necessary by users of browsers, JavaScript and C++ developers, browser implementers and specification authors for further input; to create a proper specification for the feature, and consistent implementation at browsers' source code; see How to implement option to return Blob, ArrayBuffer, or AudioBuffer from window.speechSynthesis.speak() call.
At Chromium a speech dispatcher program should be installed and the instance launched with --enable-speech-dispatcher flag set, as window.speechSynthesis.getVoices() returns an empty array, see How to use Web Speech API at chromium?.
Proof of concept
// SpeechSynthesisRecorder.js guest271314 6-17-2017
// Motivation: Get audio output from `window.speechSynthesis.speak()` call
// as `ArrayBuffer`, `AudioBuffer`, `Blob`, `MediaSource`, `MediaStream`, `ReadableStream`, or other object or data types
// See https://lists.w3.org/Archives/Public/public-speech-api/2017Jun/0000.html
// https://github.com/guest271314/SpeechSynthesisRecorder
// Configuration: Analog Stereo Duplex
// Input Devices: Monitor of Built-in Audio Analog Stereo, Built-in Audio Analog Stereo
class SpeechSynthesisRecorder {
constructor({text = "", utteranceOptions = {}, recorderOptions = {}, dataType = ""}) {
if (text === "") throw new Error("no words to synthesize");
this.dataType = dataType;
this.text = text;
this.mimeType = MediaRecorder.isTypeSupported("audio/webm; codecs=opus")
? "audio/webm; codecs=opus" : "audio/ogg; codecs=opus";
this.utterance = new SpeechSynthesisUtterance(this.text);
this.speechSynthesis = window.speechSynthesis;
this.mediaStream_ = new MediaStream();
this.mediaSource_ = new MediaSource();
this.mediaRecorder = new MediaRecorder(this.mediaStream_, {
mimeType: this.mimeType,
bitsPerSecond: 256 * 8 * 1024
});
this.audioContext = new AudioContext();
this.audioNode = new Audio();
this.chunks = Array();
if (utteranceOptions) {
if (utteranceOptions.voice) {
this.speechSynthesis.onvoiceschanged = e => {
const voice = this.speechSynthesis.getVoices().find(({
name: _name
}) => _name === utteranceOptions.voice);
this.utterance.voice = voice;
console.log(voice, this.utterance);
}
this.speechSynthesis.getVoices();
}
let {
lang, rate, pitch
} = utteranceOptions;
Object.assign(this.utterance, {
lang, rate, pitch
});
}
this.audioNode.controls = "controls";
document.body.appendChild(this.audioNode);
}
start(text = "") {
if (text) this.text = text;
if (this.text === "") throw new Error("no words to synthesize");
return navigator.mediaDevices.getUserMedia({
audio: true
})
.then(stream => new Promise(resolve => {
const track = stream.getAudioTracks()[0];
this.mediaStream_.addTrack(track);
// return the current `MediaStream`
if (this.dataType && this.dataType === "mediaStream") {
resolve({tts:this, data:this.mediaStream_});
};
this.mediaRecorder.ondataavailable = event => {
if (event.data.size > 0) {
this.chunks.push(event.data);
};
};
this.mediaRecorder.onstop = () => {
track.stop();
this.mediaStream_.getAudioTracks()[0].stop();
this.mediaStream_.removeTrack(track);
console.log(`Completed recording ${this.utterance.text}`, this.chunks);
resolve(this);
}
this.mediaRecorder.start();
this.utterance.onstart = () => {
console.log(`Starting recording SpeechSynthesisUtterance ${this.utterance.text}`);
}
this.utterance.onend = () => {
this.mediaRecorder.stop();
console.log(`Ending recording SpeechSynthesisUtterance ${this.utterance.text}`);
}
this.speechSynthesis.speak(this.utterance);
}));
}
blob() {
if (!this.chunks.length) throw new Error("no data to return");
return Promise.resolve({
tts: this,
data: this.chunks.length === 1 ? this.chunks[0] : new Blob(this.chunks, {
type: this.mimeType
})
});
}
arrayBuffer(blob) {
if (!this.chunks.length) throw new Error("no data to return");
return new Promise(resolve => {
const reader = new FileReader;
reader.onload = e => resolve(({
tts: this,
data: reader.result
}));
reader.readAsArrayBuffer(blob ? new Blob(blob, {
type: blob.type
}) : this.chunks.length === 1 ? this.chunks[0] : new Blob(this.chunks, {
type: this.mimeType
}));
});
}
audioBuffer() {
if (!this.chunks.length) throw new Error("no data to return");
return this.arrayBuffer()
.then(ab => this.audioContext.decodeAudioData(ab))
.then(buffer => ({
tts: this,
data: buffer
}))
}
mediaSource() {
if (!this.chunks.length) throw new Error("no data to return");
return this.arrayBuffer()
.then(({
data: ab
}) => new Promise((resolve, reject) => {
this.mediaSource_.onsourceended = () => resolve({
tts: this,
data: this.mediaSource_
});
this.mediaSource_.onsourceopen = () => {
if (MediaSource.isTypeSupported(this.mimeType)) {
const sourceBuffer = this.mediaSource_.addSourceBuffer(this.mimeType);
sourceBuffer.mode = "sequence"
sourceBuffer.onupdateend = () =>
this.mediaSource_.endOfStream();
sourceBuffer.appendBuffer(ab);
} else {
reject(`${this.mimeType} is not supported`)
}
}
this.audioNode.src = URL.createObjectURL(this.mediaSource_);
}));
}
readableStream({size = 1024, controllerOptions = {}, rsOptions = {}}) {
if (!this.chunks.length) throw new Error("no data to return");
const src = this.chunks.slice(0);
const chunk = size;
return Promise.resolve({
tts: this,
data: new ReadableStream(controllerOptions || {
start(controller) {
console.log(src.length);
controller.enqueue(src.splice(0, chunk))
},
pull(controller) {
if (src.length = 0) controller.close();
controller.enqueue(src.splice(0, chunk));
}
}, rsOptions)
});
}
}
Usage
let ttsRecorder = new SpeechSynthesisRecorder({
text: "The revolution will not be televised",
utternanceOptions: {
voice: "english-us espeak",
lang: "en-US",
pitch: .75,
rate: 1
}
});
// ArrayBuffer
ttsRecorder.start()
// `tts` : `SpeechSynthesisRecorder` instance, `data` : audio as `dataType` or method call result
.then(tts => tts.arrayBuffer())
.then(({tts, data}) => {
// do stuff with `ArrayBuffer`, `AudioBuffer`, `Blob`,
// `MediaSource`, `MediaStream`, `ReadableStream`
// `data` : `ArrayBuffer`
tts.audioNode.src = URL.createObjectURL(new Blob([data], {type:tts.mimeType}));
tts.audioNode.title = tts.utterance.text;
tts.audioNode.onloadedmetadata = () => {
console.log(tts.audioNode.duration);
tts.audioNode.play();
}
})
// AudioBuffer
ttsRecorder.start()
.then(tts => tts.audioBuffer())
.then(({tts, data}) => {
// `data` : `AudioBuffer`
let source = tts.audioContext.createBufferSource();
source.buffer = data;
source.connect(tts.audioContext.destination);
source.start()
})
// Blob
ttsRecorder.start()
.then(tts => tts.blob())
.then(({tts, data}) => {
// `data` : `Blob`
tts.audioNode.src = URL.createObjectURL(blob);
tts.audioNode.title = tts.utterance.text;
tts.audioNode.onloadedmetadata = () => {
console.log(tts.audioNode.duration);
tts.audioNode.play();
}
})
// ReadableStream
ttsRecorder.start()
.then(tts => tts.readableStream())
.then(({tts, data}) => {
// `data` : `ReadableStream`
console.log(tts, data);
data.getReader().read().then(({value, done}) => {
tts.audioNode.src = URL.createObjectURL(value[0]);
tts.audioNode.title = tts.utterance.text;
tts.audioNode.onloadedmetadata = () => {
console.log(tts.audioNode.duration);
tts.audioNode.play();
}
})
})
// MediaSource
ttsRecorder.start()
.then(tts => tts.mediaSource())
.then(({tts, data}) => {
console.log(tts, data);
// `data` : `MediaSource`
tts.audioNode.srcObj = data;
tts.audioNode.title = tts.utterance.text;
tts.audioNode.onloadedmetadata = () => {
console.log(tts.audioNode.dura
