mediastream-gain

cross-browser getUserMedia shim with node.js style error-first API.

npm install mediastream-gain
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mediastream-gain

What is this?

A tiny browser module for creating a gain/volume controller for the audio channels in a MediaStream.

It's useful for controlling the volume of your microphone input before it's sent accross a peer connection in a WebRTC call, for example. This module is a small part of SimpleWebRTC where it is used for minimizing echos, by using hark to determine if you're speaking and turning your mic down a bit if you're not.

This module is suitable for use with browserify/CommonJS on the client.

If you're not using browserify or you want AMD support use mediastream-volume.bundle.js.

Important details

  1. NOTE: as of this writing FireFox (while it has good WebAudio support in upcoming versions doesn't have support for using media from getUserMedia as an audio source even in its most cutting edge releases. Specifically there's no AudioContext.prototype.createMediaStreamSource. So this can't be use to mute an audio stream, for example.

  2. The way this works by replacing the first audio channel in the stream with one that is run through a gain filter. But beware that this edits the stream you give it in place it doesn't produce a new one.

Installing

npm install mediastream-gain

An example

Here we use another piece of SimpleWebRTC getusermedia to fetch user media in a cross-browser, easy-to-handle-errors-and-lack-of-support sort of way.

This assumes a commonJS environment, but that's not a requirement (see above).

var MicGainController = require('mediastream-gain');
var getUserMedia = require('getusermedia');
var gainController;

getUserMedia(function (err, stream) {
    // this will replace the audio channels in the 
    // stream
    gainController = new MicGainController(stream);
    // set gain to 20%
    gainControl.setGain(.2);
    // set gain to 0, effectively muting it
    gainControl.getGain(0); 
    // there's also:
    gainControl.off(); // equivalent to setGain(0)
    gainControl.on(); // equivalent to setGain(1)
});

Methods

It couldn't be simpler, but behavior varies slighly based on availability of WebAudio support that can be wired into WebRTC. Firefox, has WebAudio but user media can't yet be used as a source, rendering it useless for WebRTC applications.

You can check for support by checking the support property of the an instance of gainController

These will simply be noop functions if WebAudio isn't fully supported.

.setGain(Float) - takes a number between 1 and 0 .getGain() - returns current setting .off() - shortcut for turning mic off .on() - shortcut for full gain

License

MIT

Created By

If you like this, follow: @HenrikJoreteg on twitter.

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