go-gin/asset/plugins/recorder/worker.js

(function(){
    'use strict';

    importScripts('lame.min.js');

    var mp3Encoder, maxSamples = 1152, samplesMono, lame, config, dataBuffer;

    var clearBuffer = function(){
        dataBuffer = [];
    };

    var appendToBuffer = function(mp3Buf){
        dataBuffer.push(new Int8Array(mp3Buf));
    };

    var init = function(prefConfig){
        config = prefConfig || {};
        lame = new lamejs();
        mp3Encoder = new lame.Mp3Encoder(1, config.sampleRate || 44100, config.bitRate || 128);
        clearBuffer();
        self.postMessage({
            cmd: 'init'
        });
    };

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

    var convertBuffer = function(arrayBuffer){
        var data = new Float32Array(arrayBuffer);
        var out = new Int16Array(arrayBuffer.length);
        floatTo16BitPCM(data, out);
        return out;
    };

    var encode = function(arrayBuffer){
        samplesMono = convertBuffer(arrayBuffer);
        var remaining = samplesMono.length;
        for(var i = 0; remaining >= 0; i += maxSamples){
            var left = samplesMono.subarray(i, i + maxSamples);
            var mp3buf = mp3Encoder.encodeBuffer(left);
            appendToBuffer(mp3buf);
            remaining -= maxSamples;
        }
    };

    var finish = function(){
        appendToBuffer(mp3Encoder.flush());
        self.postMessage({
            cmd: 'end',
            buf: dataBuffer
        });
        clearBuffer();
    };

    self.onmessage = function(e){
        switch(e.data.cmd){
            case 'init':
                init(e.data.config);
                break;
            case 'encode':
                encode(e.data.buf);
                break;
            case 'finish':
                finish();
                break;
        }
    };
})();