@speechmatics/browser-audio-input

This package provides Javascript utilities for managing audio input devices and permissions in the browser.

It also provides utilities for capturing PCM data from these devices, if desired.

Installation

npm i @speechmatics/browser-audio-input

Usage

Querying input devices

import { getAudioDevicesStore } from "@speechmatics/browser-audio-input";
const audioDevices = getAudioDevicesStore();

audioDevices.addEventListener("changeDevices", (e) => {
  if (audioDevices.permissionState === "granted") {
    // This will print all available devices
    console.log(audioDevices.devices)
  }
});

See the README for @speechmatics/browser-audio-input-react for a complete example.

We will add non-React examples soon. If you'd like to request a specific one, feel free to file an issue!

Capturing PCM audio

To capture PCM audio, you must supply an AudioContext. From there, this library deals with dispatching audio events which can be subscribed to:

import {
  type InputAudioEvent,
  PCMRecorder,
} from '@speechmatics/browser-audio-input';

const PCMRecorder = new PCMRecorder("/path/to/pcm-audio-worklet.min.js"); // <- (see note below about this)

PCMRecorder.addEventListener('recordingStarted', () => {
  console.log("Recording started!");
});

// Later in your app...
const audioContext = new AudioContext();
pcmRecorder.startRecording({ audioContext });

Specifying input device

You can also pass a device ID like so:

import { getAudioDevicesStore } from "@speechmatics/browser-audio-input";

const audioContext = new AudioContext();

// This picks the first device ID (assuming permission has been granted)
const audioDevices = getAudioDevicesStore();
const deviceId = audioDevices.permissionState === "granted" ? audioDevices.devices[0] : undefined;
pcmRecorder.startRecording({ audioContext, deviceId });

Recording options

You can pass whatever 'MediaTrackSettings' you want through the recordingOptions property:

pcmRecorder.startRecording({
  audioContext,
  deviceId,
  recordingOptions: {
    noiseSuppression: false,
  },
});

By default we enable the following to optimize for speech:

{
  noiseSuppression: true,
  echoCancellation: true,
  autoGainControl: true,
}

Note that the last two may not be supported in Safari

Note about AudioWorklet script URL

When recording audio in the browser, there are generally three approaches:

• ❌ createScriptProcessor(): Can capture PCM data on the main thread, but is deprecated and suffers from poor performance easily.
• ❌ MediaRecorder: Provides a simple API, but cannot capture PCM data (only MPEG/OGG)
• ✅ AudioWorklet: Captures/processes PCM on dedicated thread.

This library leverages AudioWorklet to capture PCM audio (specifically 32-bit Float PCM, which is the underlying representation in the browser).

Since AudioWorklets run outside the main thread, their code must be run from an external source (i.e. a URL).

The code for this PCM audio processor is provided by this library at /dist/pcm-audio-worklet.min.js. However, how this script is loaded depends on your bundler setup.

Webpack

At the moment, Webpack doesn't have a great story for AudioWorklet scripts (see Github issue). Instead, we recommend installing the copy-webpack-plugin package to be able to copy our pcm-audio-worklet.min.js directly into your /public folder:

const CopyPlugin = require("copy-webpack-plugin");

module.exports = {
  // ... rest of your Webpack config
  plugins: [
    new CopyWebpackPlugin({
      patterns: [
        {
          from: path.resolve(
            __dirname,
            'node_modules/@speechmatics/browser-audio-input/dist/pcm-audio-worklet.min.js',
          ),
          to: path.resolve(__dirname, 'public/js/[name][ext]'),
        },
      ],
    }),
  ]
};

See Webpack documentation for more details.

Vite

Vite supports referencing bundled code by URL for use in Workers. This can be used like so:

import {
  type InputAudioEvent,
  PCMRecorder,
} from '@speechmatics/browser-audio-input';
import PCMAudioWorkletUrl from "@speechmatics/browser-audio-input/pcm-audio-worklet.min.js?url";

const PCMRecorder = new PCMRecorder(PCMAudioWorkletUrl);