a javascript module to record sound from the microphone, and save it.

AudioContextMonkeyPatch.js

/* Copyright 2013 Chris Wilson

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

/* 

This monkeypatch library is intended to be included in projects that are
written to the proper AudioContext spec (instead of webkitAudioContext), 
and that use the new naming and proper bits of the Web Audio API (e.g. 
using BufferSourceNode.start() instead of BufferSourceNode.noteOn()), but may
have to run on systems that only support the deprecated bits.

This library should be harmless to include if the browser supports 
unprefixed "AudioContext", and/or if it supports the new names.  

The patches this library handles:
if window.AudioContext is unsupported, it will be aliased to webkitAudioContext().
if AudioBufferSourceNode.start() is unimplemented, it will be routed to noteOn() or
noteGrainOn(), depending on parameters.

The following aliases only take effect if the new names are not already in place:

AudioBufferSourceNode.stop() is aliased to noteOff()
AudioContext.createGain() is aliased to createGainNode()
AudioContext.createDelay() is aliased to createDelayNode()
AudioContext.createScriptProcessor() is aliased to createJavaScriptNode()
OscillatorNode.start() is aliased to noteOn()
OscillatorNode.stop() is aliased to noteOff()
AudioParam.setTargetAtTime() is aliased to setTargetValueAtTime()

This library does NOT patch the enumerated type changes, as it is 
recommended in the specification that implementations support both integer
and string types for AudioPannerNode.panningModel, AudioPannerNode.distanceModel 
BiquadFilterNode.type and OscillatorNode.type.

*/
(function (global, exports, perf) {
  'use strict';

  function fixSetTarget(param) {
    if (!param)	// if NYI, just return
      return;
    if (!param.setTargetAtTime)
      param.setTargetAtTime = param.setTargetValueAtTime; 
  }

  if (window.hasOwnProperty('webkitAudioContext') && 
      !window.hasOwnProperty('AudioContext')) {
    window.AudioContext = webkitAudioContext;

    if (!AudioContext.prototype.hasOwnProperty('createGain'))
      AudioContext.prototype.createGain = AudioContext.prototype.createGainNode;
    if (!AudioContext.prototype.hasOwnProperty('createDelay'))
      AudioContext.prototype.createDelay = AudioContext.prototype.createDelayNode;
    if (!AudioContext.prototype.hasOwnProperty('createScriptProcessor'))
      AudioContext.prototype.createScriptProcessor = AudioContext.prototype.createJavaScriptNode;

    AudioContext.prototype.internal_createGain = AudioContext.prototype.createGain;
    AudioContext.prototype.createGain = function() { 
      var node = this.internal_createGain();
      fixSetTarget(node.gain);
      return node;
    };

    AudioContext.prototype.internal_createDelay = AudioContext.prototype.createDelay;
    AudioContext.prototype.createDelay = function(maxDelayTime) { 
      var node = maxDelayTime ? this.internal_createDelay(maxDelayTime) : this.internal_createDelay();
      fixSetTarget(node.delayTime);
      return node;
    };

    AudioContext.prototype.internal_createBufferSource = AudioContext.prototype.createBufferSource;
    AudioContext.prototype.createBufferSource = function() { 
      var node = this.internal_createBufferSource();
      if (!node.start) {
        node.start = function ( when, offset, duration ) {
          if ( offset || duration )
            this.noteGrainOn( when, offset, duration );
          else
            this.noteOn( when );
        }
      }
      if (!node.stop)
        node.stop = node.noteOff;
      fixSetTarget(node.playbackRate);
      return node;
    };

    AudioContext.prototype.internal_createDynamicsCompressor = AudioContext.prototype.createDynamicsCompressor;
    AudioContext.prototype.createDynamicsCompressor = function() { 
      var node = this.internal_createDynamicsCompressor();
      fixSetTarget(node.threshold);
      fixSetTarget(node.knee);
      fixSetTarget(node.ratio);
      fixSetTarget(node.reduction);
      fixSetTarget(node.attack);
      fixSetTarget(node.release);
      return node;
    };

    AudioContext.prototype.internal_createBiquadFilter = AudioContext.prototype.createBiquadFilter;
    AudioContext.prototype.createBiquadFilter = function() { 
      var node = this.internal_createBiquadFilter();
      fixSetTarget(node.frequency);
      fixSetTarget(node.detune);
      fixSetTarget(node.Q);
      fixSetTarget(node.gain);
      return node;
    };

    if (AudioContext.prototype.hasOwnProperty( 'createOscillator' )) {
      AudioContext.prototype.internal_createOscillator = AudioContext.prototype.createOscillator;
      AudioContext.prototype.createOscillator = function() { 
        var node = this.internal_createOscillator();
        if (!node.start)
          node.start = node.noteOn; 
        if (!node.stop)
          node.stop = node.noteOff;
        fixSetTarget(node.frequency);
        fixSetTarget(node.detune);
        return node;
      };
    }
  }
}(window));

demo.html

<!DOCTYPE html>
<html lang="en">
 <head>
  <script src="{{STATIC_URL}}js/AudioContextMonkeyPatch.js"></script>
  <script src="{{STATIC_URL}}js/recorder.js"></script>
  <script src="{{STATIC_URL}}js/main.js"></script>

  <style>
    #record.recording { 
      background: red;
      background: -webkit-radial-gradient(center, ellipse cover, #ff0000 0%,lightgrey 75%,lightgrey 100%,#7db9e8 100%); 
    }
  </style>
</head>

  <body>
    <div id="controls">
      <input id="filename" type="text" placeholder="Filename">
      <button id="record" onclick="toggleRecording(this);">record</button>
      <button id="save" onclick="saveAudio(document.getElementById('filename').value);">save</button>
    </div>
  </body>
</html>

main.js

/* Copyright 2013 Chris Wilson

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

window.AudioContext = window.AudioContext || window.webkitAudioContext;

var audioContext = new AudioContext();
var audioInput = null,
    realAudioInput = null,
    inputPoint = null,
    audioRecorder = null;
var rafID = null;
var analyserContext = null;
var recIndex = 0;

/* TODO:

- offer mono option
- "Monitor input" switch
*/

function saveAudio(file_name) {
    alert(file_name);
    filename = file_name;
    audioRecorder.exportWAV( doneEncoding );
    // could get mono instead by saying
    // audioRecorder.exportMonoWAV( doneEncoding );
}

function doneEncoding( blob ) {
    Recorder.forceDownload( blob, filename + ".wav" );
    recIndex++;
}

function toggleRecording( e ) {
    if (e.classList.contains("recording")) {
        // stop recording
        audioRecorder.stop();
        e.classList.remove("recording");
    } else {
        // start recording
        if (!audioRecorder)
            return;
        e.classList.add("recording");
        audioRecorder.clear();
        audioRecorder.record();
    }
}

function convertToMono( input ) {
    var splitter = audioContext.createChannelSplitter(2);
    var merger = audioContext.createChannelMerger(2);

    input.connect( splitter );
    splitter.connect( merger, 0, 0 );
    splitter.connect( merger, 0, 1 );
    return merger;
}

function cancelAnalyserUpdates() {
    window.cancelAnimationFrame( rafID );
    rafID = null;
}

function toggleMono() {
    if (audioInput != realAudioInput) {
        audioInput.disconnect();
        realAudioInput.disconnect();
        audioInput = realAudioInput;
    } else {
        realAudioInput.disconnect();
        audioInput = convertToMono( realAudioInput );
    }

    audioInput.connect(inputPoint);
}

function gotStream(stream) {
    inputPoint = audioContext.createGain();

    // Create an AudioNode from the stream.
    realAudioInput = audioContext.createMediaStreamSource(stream);
    audioInput = realAudioInput;
    audioInput.connect(inputPoint);

//    audioInput = convertToMono( input );

    analyserNode = audioContext.createAnalyser();
    analyserNode.fftSize = 2048;
    inputPoint.connect( analyserNode );

    audioRecorder = new Recorder( inputPoint );

    zeroGain = audioContext.createGain();
    zeroGain.gain.value = 0.0;
    inputPoint.connect( zeroGain );
    zeroGain.connect( audioContext.destination );
}

function initAudio() {
        if (!navigator.getUserMedia)
            navigator.getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
        if (!navigator.cancelAnimationFrame)
            navigator.cancelAnimationFrame = navigator.webkitCancelAnimationFrame || navigator.mozCancelAnimationFrame;
        if (!navigator.requestAnimationFrame)
            navigator.requestAnimationFrame = navigator.webkitRequestAnimationFrame || navigator.mozRequestAnimationFrame;

    navigator.getUserMedia({audio:true}, gotStream, function(e) {
            alert('Error getting audio');
            console.log(e);
        });
}

window.addEventListener('load', initAudio );

recorder.js

/*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.
*/

(function(window){

  var WORKER_PATH = '/static/js/recorderWorker.js';

  var Recorder = function(source, cfg){
    var config = cfg || {};
    var bufferLen = config.bufferLen || 4096;
    this.context = source.context;
    if(!this.context.createScriptProcessor){
       this.node = this.context.createJavaScriptNode(bufferLen, 2, 2);
    } else {
       this.node = this.context.createScriptProcessor(bufferLen, 2, 2);
    }
   // config.workerPath || WORKER_PATH
    var worker = new Worker(WORKER_PATH);
    worker.postMessage({
      command: 'init',
      config: {
        sampleRate: this.context.sampleRate
      }
    });
    var recording = false,
      currCallback;

    this.node.onaudioprocess = function(e){
      if (!recording) return;
      worker.postMessage({
        command: 'record',
        buffer: [
          e.inputBuffer.getChannelData(0),
          e.inputBuffer.getChannelData(1)
        ]
      });
    }

    this.configure = function(cfg){
      for (var prop in cfg){
        if (cfg.hasOwnProperty(prop)){
          config[prop] = cfg[prop];
        }
      }
    }

    this.record = function(){
      recording = true;
    }

    this.stop = function(){
      recording = false;
    }

    this.clear = function(){
      worker.postMessage({ command: 'clear' });
    }

    this.getBuffers = function(cb) {
      currCallback = cb || config.callback;
      worker.postMessage({ command: 'getBuffers' })
    }

    this.exportWAV = function(cb, type){
      currCallback = cb || config.callback;
      type = type || config.type || 'audio/wav';
      if (!currCallback) throw new Error('Callback not set');
      worker.postMessage({
        command: 'exportWAV',
        type: type
      });
    }

    this.exportMonoWAV = function(cb, type){
      currCallback = cb || config.callback;
      type = type || config.type || 'audio/wav';
      if (!currCallback) throw new Error('Callback not set');
      worker.postMessage({
        command: 'exportMonoWAV',
        type: type
      });
    }

    worker.onmessage = function(e){
      var blob = e.data;
      currCallback(blob);
    }

    source.connect(this.node);
    this.node.connect(this.context.destination);   // if the script node is not connected to an output the "onaudioprocess" event is not triggered in chrome.
  };

  Recorder.forceDownload = function(blob, filename){
    var url = (window.URL || window.webkitURL).createObjectURL(blob);
    var link = window.document.createElement('a');
    link.href = url;
    link.download = filename || 'output.wav';
    var click = document.createEvent("Event");
    click.initEvent("click", true, true);
    link.dispatchEvent(click);
  }

  window.Recorder = Recorder;

})(window);

recorderWorker.js

/*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.
*/

var recLength = 0,
  recBuffersL = [],
  recBuffersR = [],
  sampleRate;

this.onmessage = function(e){
  switch(e.data.command){
    case 'init':
      init(e.data.config);
      break;
    case 'record':
      record(e.data.buffer);
      break;
    case 'exportWAV':
      exportWAV(e.data.type);
      break;
    case 'exportMonoWAV':
      exportMonoWAV(e.data.type);
      break;
    case 'getBuffers':
      getBuffers();
      break;
    case 'clear':
      clear();
      break;
  }
};

function init(config){
  sampleRate = config.sampleRate;
}

function record(inputBuffer){
  recBuffersL.push(inputBuffer[0]);
  recBuffersR.push(inputBuffer[1]);
  recLength += inputBuffer[0].length;
}

function exportWAV(type){
  var bufferL = mergeBuffers(recBuffersL, recLength);
  var bufferR = mergeBuffers(recBuffersR, recLength);
  var interleaved = interleave(bufferL, bufferR);
  var dataview = encodeWAV(interleaved);
  var audioBlob = new Blob([dataview], { type: type });

  this.postMessage(audioBlob);
}

function exportMonoWAV(type){
  var bufferL = mergeBuffers(recBuffersL, recLength);
  var dataview = encodeWAV(bufferL, true);
  var audioBlob = new Blob([dataview], { type: type });

  this.postMessage(audioBlob);
}

function getBuffers() {
  var buffers = [];
  buffers.push( mergeBuffers(recBuffersL, recLength) );
  buffers.push( mergeBuffers(recBuffersR, recLength) );
  this.postMessage(buffers);
}

function clear(){
  recLength = 0;
  recBuffersL = [];
  recBuffersR = [];
}

function mergeBuffers(recBuffers, recLength){
  var result = new Float32Array(recLength);
  var offset = 0;
  for (var i = 0; i < recBuffers.length; i++){
    result.set(recBuffers[i], offset);
    offset += recBuffers[i].length;
  }
  return result;
}

function interleave(inputL, inputR){
  var length = inputL.length + inputR.length;
  var result = new Float32Array(length);

  var index = 0,
    inputIndex = 0;

  while (index < length){
    result[index++] = inputL[inputIndex];
    result[index++] = inputR[inputIndex];
    inputIndex++;
  }
  return result;
}

function floatTo16BitPCM(output, offset, input){
  for (var i = 0; i < input.length; i++, offset+=2){
    var s = Math.max(-1, Math.min(1, input[i]));
    output.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7FFF, true);
  }
}

function writeString(view, offset, string){
  for (var i = 0; i < string.length; i++){
    view.setUint8(offset + i, string.charCodeAt(i));
  }
}

function encodeWAV(samples, mono){
  var buffer = new ArrayBuffer(44 + samples.length * 2);
  var view = new DataView(buffer);

  /* RIFF identifier */
  writeString(view, 0, 'RIFF');
  /* file length */
  view.setUint32(4, 32 + samples.length * 2, true);
  /* RIFF type */
  writeString(view, 8, 'WAVE');
  /* format chunk identifier */
  writeString(view, 12, 'fmt ');
  /* format chunk length */
  view.setUint32(16, 16, true);
  /* sample format (raw) */
  view.setUint16(20, 1, true);
  /* channel count */
  view.setUint16(22, mono?1:2, true);
  /* sample rate */
  view.setUint32(24, sampleRate, true);
  /* byte rate (sample rate * block align) */
  view.setUint32(28, sampleRate * 4, true);
  /* block align (channel count * bytes per sample) */
  view.setUint16(32, 4, true);
  /* bits per sample */
  view.setUint16(34, 16, true);
  /* data chunk identifier */
  writeString(view, 36, 'data');
  /* data chunk length */
  view.setUint32(40, samples.length * 2, true);

  floatTo16BitPCM(view, 44, samples);

  return view;
}