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4.0.8 • Public • Published

Web Voice Processor

GitHub release GitHub npm

Made in Vancouver, Canada by Picovoice

A library for real-time voice processing in web browsers.

Browser compatibility

All modern browsers (Chrome/Edge/Opera, Firefox, Safari) are supported, including on mobile. Internet Explorer is not supported.

Using the Web Audio API requires a secure context (HTTPS connection), with the exception of localhost, for local development.

This library includes the utility function browserCompatibilityCheck which can be used to perform feature detection on the current browser and return an object indicating browser capabilities.


import { browserCompatibilityCheck } from '@picovoice/web-voice-processor';



Browser features

  • '_picovoice' : whether all Picovoice requirements are met
  • 'AudioWorklet' (not currently used; intended for the future)
  • 'isSecureContext' (required for microphone permission for non-localhost)
  • 'mediaDevices' (basis for microphone enumeration / access)
  • 'WebAssembly' (required for all Picovoice engines)
  • 'webKitGetUserMedia' (legacy predecessor to getUserMedia)
  • 'Worker' (required for resampler and for all engine processing)


npm install @picovoice/web-voice-processor


yarn add @picovoice/web-voice-processor

How to use

Via ES Modules (Create React App, Angular, Webpack, etc.)

import { WebVoiceProcessor } from '@picovoice/web-voice-processor';

Via HTML script tag

Add the following to your HTML:

<script src="@picovoice/web-voice-processor/dist/iife/index.js"></script>

The IIFE version of the library adds WebVoiceProcessor to the window global scope.

Start listening

WebVoiceProcessor follows the subscribe/unsubscribe pattern. WebVoiceProcessor will automatically start recording audio as soon as an engine is subscribed.

const worker = new Worker('${WORKER_PATH}');
const engine = {
  onmessage: function(e) {
    /// ... handle inputFrame

await WebVoiceProcessor.subscribe(engine);
await WebVoiceProcessor.subscribe(worker);
// or
await WebVoiceProcessor.subscribe([engine, worker]);

An engine is either a Web Workers or an object implementing the following interface within their onmessage method:

onmessage = function (e) {
    switch (e.data.command) {
        case 'process':

where e.data.inputFrame is an Int16Array of frameLength audio samples.

For examples of using engines, look at src/engines.

This is async due to its Web Audio API microphone request. The promise will be rejected if the user refuses permission, no suitable devices are found, etc. Your calling code should anticipate the possibility of rejection. When the promise resolves, the WebVoiceProcessor is running.

Stop Listening

Unsubscribing the engines initially subscribed will stop audio recorder.

await WebVoiceProcessor.unsubscribe(engine);
await WebVoiceProcessor.unsubscribe(worker);
await WebVoiceProcessor.unsubscribe([engine, worker]);


Use the reset function to remove all engines and stop recording audio.

await WebVoiceProcessor.reset();


To update the audio settings in WebVoiceProcessor, use the setOptions function:

// Override default options
let options = {
  frameLength: 512,
  outputSampleRate: 16000,
  deviceId: null,
  filterOrder: 50



WebVoiceProcessor includes a built-in engine which returns the VU meter. To capture the VU meter value, create a VuMeterEngine instance and subscribe it to the engine:

function vuMeterCallback(dB) {

const vuMeterEngine = new VuMeterEngine(vuMeterCallback);

The vuMeterCallback should expected a number in terms of dBFS within the range of [-96, 0].

Build from source

Use yarn or npm to build WebVoiceProcessor:

yarn build


npm install
npm run-script build

The build script outputs minified and non-minified versions of the IIFE and ESM formats to the dist folder. It also will output the TypeScript type definitions.

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npm i @picovoice/web-voice-processor

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