nodewave.js

var sys = require('sys');
var http = require('http');
var buffer = require('buffer');
var child_process = require('child_process');

var Buffer = buffer.Buffer;

var PORT = 8765;
var SAMPLE_RATE = 44100;
var CHUNK_SIZE = 4410; // why did I choose this??

function fix(x) { return ((2<<14)*x)|0; }
function hi(word) { return (word & 0xff00)>>8; }
function lo(word) { return word & 0xff; }

function radiansPerSample(freq) { return 2*Math.PI*freq/SAMPLE_RATE; }
function mtof(pitch) { return Math.pow(2.0, (pitch-69)/12.0)*440.0; }

var server = http.createServer(handle);

server.listen(PORT);
sys.puts('started on port '+PORT);


var lame = child_process.spawn('lame', ['-r','-m','m','-b','32','-','-']);

setInterval(render, 1000*CHUNK_SIZE/SAMPLE_RATE);

var bytes = new Buffer(2*CHUNK_SIZE); // 16-bit samples
var sample = 0;
function render() {
  var pitch = Math.random()<0.25 ? 72 : (Math.random()<0.5?60:64);
  var k = radiansPerSample(mtof(pitch));
  for(var i = 0; i < CHUNK_SIZE; i++) {
    sample++;
    var fixed = fix(Math.sin(k*sample)>0?0.5:-0.5);
    bytes[2*i+0] = lo(fixed);
    bytes[2*i+1] = hi(fixed);
  }

  lame.stdin.write(bytes);
}

function handle(request, response) {
  sys.puts('client connected from '+request.connection.remoteAddress);
  response.writeHead(200, {'content-type': 'audio/mpeg'});

  function send(data) { response.write(data); }

  lame.stdout.addListener('data', send);

  request.connection.addListener('end', function() {
    sys.puts('client disconnected from '+request.connection.remoteAddress);
    lame.stdout.removeListener('data', response.write);
    response.end();
  });
}