Audio Recorder Polyfill

src="./logo.svg"
title="Audio Recorder Polyfill Logo">

[MediaRecorder] polyfill to record audio in Edge and Safari.
Try it in [online demo] and see [API].

* Spec compatible. In the future when all browsers will support
MediaRecorder, you will remove polyfill.
* Small. 1.11 KB (minified and gzipped). No dependencies.
It uses [Size Limit] to control size.
* One file. In contrast to other recorders, this polyfill uses
“inline worker” and don’t need a separated file for Web Worker.
* MP3 and WAV encoder support.

``js
navigator.mediaDevices.getUserMedia({ audio: true }).then(stream => {
recorder = new MediaRecorder(stream)
recorder.addEventListener('dataavailable', e => {
audio.src = URL.createObjectURL(e.data)
})
recorder.start()
})
`

[MediaRecorder]: https://developers.google.com/web/updates/2016/01/mediarecorder
[online demo]: https://ai.github.io/audio-recorder-polyfill/
[Size Limit]: https://github.com/ai/size-limit
[API]: https://ai.github.io/audio-recorder-polyfill/api/


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Install

Install package:

`sh
npm install --save audio-recorder-polyfill
`

We recommend creating separated webpack/Parcel bundle with polyfill.
In this case, polyfill will be downloaded only by Edge and Safari.
Good browsers will download less.

Files recorded without the polyfill will not be playable on Safari,
it is highly recommended to convert it to MP3 on the back-end
of your application. If that’s not an option you can use the polyfill
in all browsers to force the audio to be converted to the right format
with the price of client’s performance.

`diff
entry: {
app: './src/app.js',
+ polyfill: './src/polyfill.js'
}
`

Install polyfill as MediaRecorder in this new bundle src/polyfill.js:

`js
import AudioRecorder from 'audio-recorder-polyfill'
window.MediaRecorder = AudioRecorder
`

Add this code to your HTML to load this new bundle only for browsers
without MediaRecorder support:

`diff
+

`

ES Modules

Polyfill supports ES modules. You do not need to do anything for bundlers.

For quick hacks you can load polyfill from CDN. Do not use it in production
because of low performance.

`js
import AudioRecorder from 'https://cdn.jsdelivr.net/npm/audio-recorder-polyfill/index.js'
window.MediaRecorder = AudioRecorder
`

Usage

In the beginning, we need to show a warning in browsers without Web Audio API:

`js
if (MediaRecorder.notSupported) {
noSupport.style.display = 'block'
dictaphone.style.display = 'none'
}
`

Then you can use standard MediaRecorder [API]:

`js
let recorder

recordButton.addEventListener('click', () => {
// Request permissions to record audio
navigator.mediaDevices.getUserMedia({ audio: true }).then(stream => {
recorder = new MediaRecorder(stream)

// Set record to

// Start recording
recorder.start()
})
})

stopButton.addEventListener('click', () => {
// Stop recording
recorder.stop()
// Remove “recording” icon from browser tab
recorder.stream.getTracks().forEach(i => i.stop())
})
`

If you need to upload record to the server, we recommend using timeslice.
MediaRecorder will send recorded data every specified millisecond.
So you will start uploading before recording would finish.

`js
// Will be executed every second with next part of audio file
recorder.addEventListener('dataavailable', e => {
sendNextPiece(e.data)
})
// Dump audio data every second
recorder.start(1000)
`

[API]: https://developer.mozilla.org/en-US/docs/Web/API/MediaStream_Recording_API/Using_the_MediaStream_Recording_API

Audio Formats

Chrome records natively only to .webm files. Firefox to .ogg.

You can get used file format in e.data.type:

`js
recorder.addEventListener('dataavailable', e => {
e.data.type //=> 'audio/wav' with polyfill
// 'audio/webm' in Chrome
// 'audio/ogg' in Firefox
})
`

$3

As default, this polyfill saves records to .wav files. Compression
is not very good, but encoding is fast and simple.

$3

For better compression you may use the MP3 encoder.

`js
import AudioRecorder from 'audio-recorder-polyfill'
import mpegEncoder from 'audio-recorder-polyfill/mpeg-encoder'

AudioRecorder.encoder = mpegEncoder
AudioRecorder.prototype.mimeType = 'audio/mpeg'
window.MediaRecorder = AudioRecorder
`

Limitations

This polyfill tries to be MediaRecorder API compatible.
But it still has small differences.

* WAV format contains duration in the file header. As result, with timeslice
or requestData() call, dataavailable will receive a separated file
with header on every call. In contrast, MediaRecorder sends header only
to first dataavailable. Other events receive addition bytes
to the same file.
* Constructor options are not supported.
* BlobEvent.timecode is not supported.

Custom Encoder

If you need audio format with better compression,
you can change polyfill’s encoder:

`diff
import AudioRecorder from 'audio-recorder-polyfill'
+ import customEncoder from './ogg-opus-encoder'
+
+ AudioRecorder.encoder = customEncoder
+ AudioRecorder.prototype.mimeType = 'audio/ogg'
window.MediaRecorder = AudioRecorder
`

The encoder should be a function with Web Worker in the body.
Polyfill converts function to the string to make Web Worker.

`js
module.exports = () => {
function init (sampleRate) {
…
}

function encode (input) {
…
}

function dump (sampleRate) {
…
postMessage(output)
}

onmessage = e => {
if (e.data[0] === 'init') {
init(e.data[1])
} else if (e.data[0] === 'encode') {
encode(e.data[1])
} else if (e.data[0] === 'dump') {
dump(e.data[1])
}
}
}
``