Audio Recorder Polyfill
MediaRecorder
polyfill to record audio in Edge and Safari 11.
It uses Web Audio API and WAV encoder in Web Worker.
Try it in online demo.
- Spec compatible. In the future when other browsers will support
MediaRecorder
, you will be able to remove polyfill. - Small. Less than 1 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.
navigator.mediaDevices.getUserMedia({ audio: true }).then(stream => {
recorder = new MediaRecorder(stream)
recorder.addEventListener('dataavailable', e => {
audio.src = URL.createObjectURL(e.data)
})
recorder.start()
})
Install
Install package:
npm install --save audio-recorder-polyfill
We recommend creating separated webpack bundle with polyfill. In this case,
polyfill will be downloaded only by Edge and Safari. Good browsers will
download less.
entry: {
app: './src/app.js',
+ polyfill: './src/polyfill.js'
}
Install polyfill as MediaRecorder
in this new bundle src/polyfill.js
:
window.MediaRecorder = require('audio-recorder-polyfill')
Add this code to your HTML to load this new bundle only for browsers
without MediaRecorder
support:
+ <script>
+ if (!window.MediaRecorder) {
+ document.write(unescape('%3Cscript src="/polyfill.js">%3C/script>'))
+ }
+ </script>
<script src="/app.js" defer></script>
Usage
In the begging, we need to show a warning in browsers without Web Audio API:
if (MediaRecorder.notSupported) {
noSupport.style.display = 'block'
dictaphone.style.display = 'none'
}
Then you can use standard MediaRecorder
API:
let recorder
recordButton.addEventListener('click', () => {
navigator.mediaDevices.getUserMedia({ audio: true }).then(stream => {
recorder = new MediaRecorder(stream)
recorder.addEventListener('dataavailable', e => {
audio.src = URL.createObjectURL(e.data)
})
recorder.start()
})
})
stopButton.addEventListener('click', () => {
recorder.stop()
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.
recorder.addEventListener('dataavailable', e => {
sendNextPiece(e.data)
})
recorder.start(1000)
Audio Formats
Chrome records natively only to .webm
files. Firefox to .ogg
.
This polyfill saves records to .wav
files. Compression
is not very good, but encoding is fast and simple.
You can get used file format in e.data.type
:
recorder.addEventListener('dataavailable', e => {
e.data.type
})
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.
- Polyfill ignores method call in the wrong state (like
stop()
during inactive
state) instead of throwing an error. BlobEvent.timecode
is not supported.
Custom Encoder
If you need audio format with better compression,
you can change polyfill’s encoder:
window.MediaRecorder = require('audio-recorder-polyfill')
+ MediaRecorder.encoder = require('./ogg-opus-encoder')
+ MediaRecorder.mimeType = 'audio/ogg'
The encoder should be a function with Web Worker in the body.
Polyfill converts function to the string to make Web Worker.
module.exports = function () {
function encode (input) {
…
}
function dump (sampleRate) {
…
postMessage(output)
}
onmessage = function (e) {
if (e.data[0] === 'encode') {
encode(e.data[1])
} else {
dump(e.data[1])
}
}
}