Programatically Mixdown of audio tracks (no playback)

Question

Hi,

I've found some excellent demos of how to mix together sound objects together for live playback. See the working example bellow...

But can it be done programatically without any playback so I can just output the mixed file? Also I'll be adding some volume change info along the way so it'll need to be added in small chunks like how the play buffer works.

Any help will be gratefully received, Thanks

            [Embed(source = "audio/track01.mp3")] 
            private var Track1:Class;       
            [Embed(source = "audio/track02.mp3")] 
            private var Track2:Class;       
            [Embed(source = "audio/track03.mp3")] 
            private var Track3:Class;
            [Embed(source = "audio/track04.mp3")] 
            private var Track4:Class;[Embed(source = "AudioMixerFilter2.pbj",mimeType = "application/octet-stream")]
            private var EmbedShader:Class;

            private var shader:Shader = new Shader(new EmbedShader());

            private var sound:Vector.<Sound> = new Vector.<Sound>();    
            private var bytes:Vector.<ByteArray> = new Vector.<ByteArray>();
            private var sliders:Vector.<Number> = new Vector.<Number>();

            private var sliderVol:int = 1;

            private var BUFFER_SIZE:int = 0x800;

            public var playback:Sound = new Sound();

            public function startAudioMixer(event:FlexEvent):void{


                sound.push(new Track1(), new Track2(), new Track3(), new Track4());
                sliders.push(sliderVol,sliderVol,sliderVol,sliderVol);

                playback.addEventListener(SampleDataEvent.SAMPLE_DATA, onSoundData);
                playback.play();
            }

            private function onSoundData(event:SampleDataEvent):void {

                for(var i:int = 0; i < sound.length; i++){
                    bytes[i] = new ByteArray();
                    bytes[i].length = BUFFER_SIZE * 4 * 2;
                    sound[i].extract(bytes[i], BUFFER_SIZE);                

                    var volume:Number = 0;
                    bytes[i].position = 0;  

                    for(var j:int = 0; j < BUFFER_SIZE; j++){
                        volume += Math.abs(bytes[i].readFloat());
                        volume += Math.abs(bytes[i].readFloat());                   
                    }



                    volume = (volume / (BUFFER_SIZE * .5)) * sliderVol; // SLIDER VOL WILL CHANGE       

                    shader.data['track' + (i + 1)].width    = BUFFER_SIZE / 1024;
                    shader.data['track' + (i + 1)].height   = 512;
                    shader.data['track' + (i + 1)].input    = bytes[i];
                    shader.data['vol'   + (i + 1)].value    = [sliders[i]];

                }

                var shaderJob:ShaderJob = new ShaderJob(shader,event.data,BUFFER_SIZE / 1024,512);
                shaderJob.start(true);
            }