welll/record-encode-audio-from-browser

importScripts('libmp3lame.js');

var mp3codec;

var recLength = 0,
    recBuffers = [];

//https://github.com/gypified/libmp3lame/blob/master/API

self.onmessage = function(e) {

    switch (e.data.command) {

        case 'init':
            init(e.data.config);
            break;
        case 'encode':
            encode(e);
            break;
        case 'finish':
            finish();
            break;
    }
};

function init(config) {

    if (!config) {
        config = {};
    }

    mp3codec = Lame.init();

    Lame.set_mode(mp3codec, config.mode || Lame.JOINT_STEREO);
    Lame.set_num_channels(mp3codec, config.channels || 2);
    Lame.set_out_samplerate(mp3codec, config.samplerate || 44100);
    Lame.set_in_samplerate(mp3codec, config.in_samplerate || 44100);
    /*The default is a  J-Stereo, 44.1khz, 128kbps CBR mp3 file at quality 5.*/
    Lame.set_bitrate(mp3codec, config.bitrate || 128);

    //Lame.set_mode(mp3codec, 1);
    //lame.set_quality(mp3codec,2);   /* 2=high  5 = medium  7=low */ 
    //Lame.set_num_samples(mp3codec, e.data.config.samples || -1);

    Lame.init_params(mp3codec);

    // console.log('Version :', Lame.get_version() + ' / ',
    //     'Mode: ' + Lame.get_mode(mp3codec) + ' / ',
    //     'Samples: ' + Lame.get_num_samples(mp3codec) + ' / ',
    //     'Channels: ' + Lame.get_num_channels(mp3codec) + ' / ',
    //     'Input Samplate: ' + Lame.get_in_samplerate(mp3codec) + ' / ',
    //     'Output Samplate: ' + Lame.get_in_samplerate(mp3codec) + ' / ',
    //     'Bitlate :' + Lame.get_bitrate(mp3codec) + ' / ',
    //     'VBR :' + Lame.get_VBR(mp3codec));

}

function encode(e) {

    var mp3data = Lame.encode_buffer_ieee_float(mp3codec, e.data.buf, e.data.buf);

    //self.postMessage({
    //    command: 'data',
    //    buf: mp3data.data
    //});

    ///console.log(mp3data.data.toString('hex'));

    recBuffers.push(mp3data.data);
    recLength += mp3data.data.length;

}

function finish() {

    //console.log('recBuffers.length:' + recBuffers.length);
    //console.log('recLength:' + recLength);

    var mp3data = Lame.encode_flush(mp3codec);

    recBuffers.push(mp3data.data);
    recLength += mp3data.data.length;

    self.postMessage({
        command: 'data',
        buf: mp3data.data
    });

    var buffer = mergeBuffers(recBuffers, recLength);
    //buffer = new ArrayBuffer(buffer.length);
    var view = new Uint8Array(buffer);

    var audioBlob = new Blob([view], {
        type: "audio/mp3"
    });

    self.postMessage({
        command: 'mp3',
        buf: audioBlob
    });

    Lame.close(mp3codec);
    mp3codec = null;

    recBuffers = [];
    recLength = 0;
}

function mergeBuffers(recBuffers, recLength) {
    //Float32Array
    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;

}