How do I convert an array of audio data into a wav file?

I have a feature that records audio annotations for a user. It uses HTML5 with a flash fallback. I am able to get the audio data from the HTML5 version via getUserMedia(), but the flash fallback provides the data as an array of floats.

I need this data as a wav file, and I can't figure out how to do it. Any help much appreciated!

Answers:

Answer
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 'getBuffer':
        getBuffer();
        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 getBuffer() {
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) {
var buffer = new ArrayBuffer(44 + samples.length * 2);
var view = new DataView(buffer);

writeString(view, 0, 'RIFF');
view.setUint32(4, 32 + samples.length * 2, true);
writeString(view, 8, 'WAVE');
writeString(view, 12, 'fmt ');
view.setUint32(16, 16, true);
view.setUint16(20, 1, true);
view.setUint16(22, 2, true);
view.setUint32(24, sampleRate, true);
view.setUint32(28, sampleRate * 4, true);
view.setUint16(32, 4, true);
view.setUint16(34, 16, true);
writeString(view, 36, 'data');
view.setUint32(40, samples.length * 2, true);

floatTo16BitPCM(view, 44, samples);

return view;
}

usage:

var AudioContext = win.webkitAudioContext,
    recorder, audioContext;


function recordAudio() {
    if (!config.stream) {
        alert('No audio.');
        return;
    }
    initAudioRecorder(config.audioWorkerPath);
    audioContext = new AudioContext;
    var mediaStreamSource = audioContext.createMediaStreamSource(config.stream);

    mediaStreamSource.connect(audioContext.destination);
    recorder = new window.Recorder(mediaStreamSource);

    recorder && recorder.record();
}

function stopAudioRecording() {
    console.warn('Audio recording stopeed');
    recorder && recorder.stop();
    recorder && recorder.exportWAV(function (blob) {
        fileType = 'wav';
        setBlob(blob);
    });
    recorder && recorder.clear();
}

var writer;

function setBlob(blob) {
    blobURL = blob;

    var config = {
        blob: blobURL,
        type: 'audio/wav',
        fileName: (Math.random() * 1000 << 1000) + '.' + fileType,
        size: blobURL.length
    };
    writer = RecordRTCFileWriter(config);

    var reader = new win.FileReader();
    reader.readAsDataURL(blobURL);
    reader.onload = function (event) {
        blobURL2 = event.target.result;
    };
}

return {
    stopAudio: stopAudioRecording,
    stopVideo: stopVideoRecording,
    recordVideo: recordVideo,
    recordAudio: recordAudio,
    save: saveToDisk,
    getBlob: function () {
        return blobURL2;
    },
    toURL: function () {
        return writer.toURL();
    }
};

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