Microphone input to MP3

mic.js

// Uses getUserMedia to record audio from microphone, compresses it to mp3, and throws it away.
// You should change the last step to e.g. pushing the audio to a server over a WebSocket.

// This script uses lame.js for mp3 encoding
// https://github.com/zhuker/lamejs

var audioDataCallback = function(encodedData, originalData) {
    console.log("Encoded " + encodedData.byteLength + " bytes. Original: " + originalData.byteLength);
};

var channels = 1; // 1 for mono or 2 for stereo
var sampleRate = 44100; // 44.1khz (normal mp3 samplerate)
var kbps = 128; // encode 128kbps mp3
var mp3encoder = new lamejs.Mp3Encoder(channels, sampleRate, kbps);

var BUFF_SIZE = 2048; // 2k buffer for GUM, needs to be power of two

var samples = new Int16Array(BUFF_SIZE);
var sampleBlockSize = 576; // can be anything but make it a multiple of 576 to make encoder's life easier

var audioContext = new AudioContext();

if (!navigator.getUserMedia) {
    navigator.getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia ||
    navigator.mozGetUserMedia || navigator.msGetUserMedia;
}

if (navigator.getUserMedia) {

    navigator.getUserMedia(
        {
            audio: {
                echoCancellation: true,
                noiseSuppression: true,
                autoGainControl: true
            }
        },
        function(stream) {
            start_microphone(stream);
        },
        function(e) {
            console.log('Error capturing audio.', e);
        }
    );

} else {
    console.log('getUserMedia not supported in this browser.');
}

function start_microphone(stream){
    console.log('mic started');

    var gain_node = audioContext.createGain();
    gain_node.connect( audioContext.destination );
    gain_node.gain.value = 0;

    var microphone_stream = audioContext.createMediaStreamSource(stream);

    var script_processor_node = audioContext.createScriptProcessor(BUFF_SIZE, 1, 1);
    script_processor_node.onaudioprocess = process_microphone_buffer;

    microphone_stream.connect(script_processor_node);
    script_processor_node.connect(gain_node);
}


var sampleI16 = new Int16Array(BUFF_SIZE);
function process_microphone_buffer(event) {
    var sample = event.inputBuffer.getChannelData(0);

    /* Send raw data
    for (var j = 0; j < sample.length; j++) {
        sampleI16[j] = sample[j] * 10 * 0x7FF;
    }
    audioDataCallback(sampleI16, sampleI16);
    */

    /* MP3 encode */
    for (var j = 0; j < sample.length; j += sampleBlockSize) {
        var sampleBlock = sample.slice(j, j+sampleBlockSize);
        var sampleI16 = new Int16Array(sampleBlock.length);
        for (var i = 0; i < sampleBlock.length; i++) {
            sampleI16[i] = sampleBlock[i] * 10 * 0x7FF; // Convert float to int16 with 10x gain
        }
        var mp3 = mp3encoder.encodeBuffer(sampleI16);
        if (mp3.length > 0) {
            audioDataCallback(mp3, sampleI16);
        }
    }
}