mixing 2 sounds from ByteArray - actionscript-3

Question

I have build a mixer and save all the sequence in an array and then play it again, now I want to save the mix as an MP3, I have looked for any way to save the mix and the answer is to load the sounds as byteArrays (sound.extract) I have acomplish that but I don't really know how to store all the sounds in just one ByteArray in order to save it as MP3, I got this code just for example, loading 2 audio files and store them in separate ByteArrays, and play each sound, does any body know how to store the 2 byteArrays in just one?
var mySound:Sound = new Sound();
var sourceSnd:Sound = new Sound();
var urlReq:URLRequest = new URLRequest("Track1.mp3");
sourceSnd.load(urlReq);
sourceSnd.addEventListener(Event.COMPLETE, loaded);
function loaded(event:Event):void
{
mySound.addEventListener(SampleDataEvent.SAMPLE_DATA, processSound);
//mySound.play();
}
var mySound2:Sound = new Sound();
var sourceSnd2:Sound = new Sound();
var urlReq2:URLRequest = new URLRequest("Track2.mp3");
sourceSnd2.load(urlReq2);
sourceSnd2.addEventListener(Event.COMPLETE, loaded2);
function loaded2(event:Event):void
{
mySound2.addEventListener(SampleDataEvent.SAMPLE_DATA, processSound2);
mySound2.play();
mySound.play();
}
function processSound(event:SampleDataEvent):void
{
var bytes:ByteArray = new ByteArray();
sourceSnd.extract(bytes, 8192);
event.data.writeBytes(bytes);
}
function processSound2(event:SampleDataEvent):void
{
var bytes:ByteArray = new ByteArray();
sourceSnd2.extract(bytes, 8192);
event.data.writeBytes(bytes);
}

Answer 1

been working on a similar system for a while, I'll do my best to give you some direction:
Your example code is not really mixing the MP3's - it's creating 2 more sounds to playback the loaded MP3's via the SampleDataEvent. What you need to do is create just one "output" Sound file that will hold/playback the resulting mixed sound. You can easily save that data as it happens and subsequently save that file as a new WAV/MP3/what-have-you.
real/psuedo-code (read:lazy) :
output = new Sound();
output.addEventListener( SampleDataEvent.SAMPLE_DATA , mixAudio );
song1 = new Sound / load the first mp3
song2 = new Sound / load the second mp3
// a byteArray for "recording" the output and subsequent file creation
recordedBytes = new ByteArray();
either wait until both mp3's are completely loaded, or run an enter-frame to determine when both Sounds are no longer buffering (Sound.isBuffering )
when the mp3's are ready:
// numbers to store some values
var left1:Number;
var right1:Number;
var left2:Number;
var right2:Number;
// bytearrays for extracting and mixing
var bytes1:ByteArray = new ByteArray( );
var bytes2:ByteArray = new ByteArray( );
// start the show
output.play();
function mixAudio( e:SampleDataEvent ):void{
//set bytearray positions to 0
bytes1.position = 0;
bytes2.position = 0;
//extract
song1.extract( bytes1, 8192 );
song2.extract( bytes2, 8192 );
// reset bytearray positions to 0 for reading the floats
bytes1.position = 0;
bytes2.position = 0;
// run through all the bytes/floats
var b:int = 0;
while( b < 8192 ){
left1 = bytes1.readFloat(); // gets "left" signal
right1 = bytes1.readFloat(); // gets "right" signal
left2 = bytes2.readFloat();
right2 = bytes2.readFloat();
// mix!
var newLeft:Number = ( left1 + left2 ) * .5;
var newRight:Number = ( right1 + right2 ) * .5;
// write the new stuff to the output sound's
e.data.writeFloat( newLeft );
e.data.writeFloat( newRight );
// write numbers to the "recording" byteArray
recordedBytes.writeFloat( newLeft );
recordedBytes.writeFloat( newRight );
b++;
}
}
Yes - you should really cap the possible output at -1/1. Do it. This is extremely un-optimized!
Ok. so that's the easy part! The tough part is really converting the final byteArray to MP3. The audio exists within Flash as PCM/uncompressed data, MP3 is obviously a compressed format. This "answer" is already way too long and all this info I've gleaned from several very smart folks.
You can easily adapt 'MicRecorder' to be a generic Sound data recorder:
http://www.bytearray.org/?p=1858
converting to MP3 will be a bitch: Thibault has another post on ByteArray.org - search for LAME MP3.
Excellent example/resource:
http://www.anttikupila.com/flash/soundfx-out-of-the-box-audio-filters-with-actionscript-3/
Look up Andre Michelle's open source 'Tonfall' project on Google code.
Look up Kevin Goldsmith's blog and labs - he's got great example on utilizing Pixel Bender with all this madness.
hope this helps!
PS - taking a cue from Andre, the optimal length of the audio buffer should be 3072. Give it a try on your machine!

Answer 2

If I understand your question properly, you need read the floating point data for each sample, sum them, and write the resulting value into your new audio stream. This would give a stright 50/50 mix.
I don't have access to a machine with a compiler right now, but it should be something like this (assuming bytes1 and bytes2 are two ByteArray objects of equal length):
for (int bcnt = bytes1.size(); bcnt; bcnt--)
bytes1.setByte(bcnt - 1, bytes2.getByte(bcnt - 1) + bytes1.getByte(bcnt - 1));
Of course, you would probably want to do some sort of overflow check, but that should be enough to put you on the right track.

Answer 3

if you have uncompressed audio, you can just add up the values of individual array elements in your ByteArray's. But you also have to handle capping for max/min values (no overflows). Pretty sure there is nothing equivalent for mixing MP3s - so you might have to decode, mix, and encode to MP3 again.