Recorder.js

A plugin for recording/exporting the output of Web Audio API nodes

Note: This repository a fork of Recorder.js, because the original repository is no longer maintained. Thanks to Matt Diamond for his great work.

They only change here is that users using this lib can export the wav file with specific sample rate. See this issue for more details. I fail to find any other forks with sample rate support, so I decide to fork it and apply the changes in the previous issue. Thanks to QiaoZhong for the solution.

Installation

npm install recorderjs-ex

Usage

if you don't want to read the whole document, you can just read the following demo code, which is easy to understood

// initialize the recorder
const stream = await navigator.mediaDevices.getUserMedia({ audio: true });
const audioContext = new AudioContext({});
const input = audioContext.createMediaStreamSource(stream);
const recorder = new Recorder(input, {
	// we can change the channels, default is 2
	numChannels: 1,
});

// start to record
recorder.record();

// stop to record, maybe user clicks a stop button
recorder.stop();

// get the audio with the sample rate we want (here is 8000, you can pass 16000)
recorder.exportWAV((blob: Blob) => {
	// do something with the blob
}, 'audio/wav', 8000);

Syntax

Constructor

var rec = new Recorder(source [, config])

Creates a recorder instance.

• source - The node whose output you wish to capture
• config - (optional) A configuration object (see config section below)

Config

• workerPath - Path to recorder.js worker script. Defaults to 'js/recorderjs/recorderWorker.js'
• bufferLen - The length of the buffer that the internal JavaScriptNode uses to capture the audio. Can be tweaked if experiencing performance issues. Defaults to 4096.
• callback - A default callback to be used with exportWAV.
• type - The type of the Blob generated by exportWAV. Defaults to 'audio/wav'.

Instance Methods

rec.record()
rec.stop()

Pretty self-explanatory... record will begin capturing audio and stop will cease capturing audio. Subsequent calls to record will add to the current recording.

rec.clear()

This will clear the recording.

rec.exportWAV([callback][, type, targetSampleRate])

This will generate a Blob object containing the recording in WAV format. The callback will be called with the Blob as its sole argument. If a callback is not specified, the default callback (as defined in the config) will be used. If no default has been set, an error will be thrown.

In addition, you may specify the type of Blob to be returned (defaults to 'audio/wav').

rec.getBuffer([callback])

This will pass the recorded stereo buffer (as an array of two Float32Arrays, for the separate left and right channels) to the callback. It can be played back by creating a new source buffer and setting these buffers as the separate channel data:

function getBufferCallback( buffers ) {
	var newSource = audioContext.createBufferSource();
	var newBuffer = audioContext.createBuffer( 2, buffers[0].length, audioContext.sampleRate );
	newBuffer.getChannelData(0).set(buffers[0]);
	newBuffer.getChannelData(1).set(buffers[1]);
	newSource.buffer = newBuffer;

	newSource.connect( audioContext.destination );
	newSource.start(0);
}

This sample code will play back the stereo buffer.

rec.configure(config)

This will set the configuration for Recorder by passing in a config object.

Utility Methods (static)

Recorder.forceDownload(blob[, filename])

This method will force a download using the new anchor link download attribute. Filename defaults to 'output.wav'.

License (MIT)

Copyright © 2013 Matt Diamond

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.