node.js

var midi = require("midi")
var Through = require('through')

module.exports = function(name, opts){
  var stream = Through(write, end)

  stream.close = stream.end

  var input = stream.inputPort = getInput(name, opts)
  var output = stream.outputPort = getOutput(name, opts)

  if (!input || !output){
    stream.emit('error', new Error('No midi device found with name ' + name))
  }

  input.on('message', function(deltaTime, data){
    if (opts && opts.normalizeNotes) {
      data = normalizeNotes(data)
    }
    stream.queue(data)
  })

  function write(data){
    output.sendMessage(data)
    this.emit('send', data)
  }

  function end(){
    this.queue(null)
    input.closePort()
    output.closePort()
  }

  return stream
}

module.exports.openInput = function(name, opts){
  var stream = Through(function () {}, end)
  var input = stream.inputPort = getInput(name, opts)

  if (!input){
    stream.emit('error', new Error('No midi device found with name ' + name))
  }

  input.on('message', function(deltaTime, data){
    if (opts && opts.normalizeNotes) {
      data = normalizeNotes(data)
    }
    stream.queue(data)
  })

  function end(){
    this.queue(null)
    input.closePort()
  }

  return stream
}

module.exports.openOutput = function(name, opts){
  var stream = Through(write, end)
  var output = stream.outputPort = getOutput(name, opts)

  if (!output){
    stream.emit('error', new Error('No midi device found with name ' + name))
  }

  function write(data){
    output.sendMessage(data)
    this.emit('send', data)
  }

  function end(){
    this.queue(null)
    output.closePort()
  }

  return stream
}

module.exports.getPortNames = function(cb){
  var used = {}
  var names = {}

  process.nextTick(function() {
    try {
      var input = new midi.input()
      var count = input.getPortCount()
      for (var i=0;i < count;i++){
        var name = input.getPortName(i)
        if (used[name]){
          var i = used[name] += 1
          names[name + '/' + i] = true
        } else {
          used[name] = 1
          names[name] = true
        }
      }

      used = {}
      var output = new midi.output()
      var count = output.getPortCount()
      for (var i=0;i < count;i++){
        var name = output.getPortName(i)
        if (used[name]){
          var i = used[name] += 1
          names[name + '/' + i] = true
        } else {
          used[name] = 1
          names[name] = true
        }
      }

      cb&&cb(null, Object.keys(names))
    } catch (ex){
      cb&&cb(ex)
    }
  })
}

function getInput(name, opts){
  if (typeof opts === 'number') opts = {index: opts}
  var index = opts && opts.index || 0
  var ignoreTiming = !opts || !opts.includeTiming
  var port = new midi.input()
  if (opts && opts.virtual){
    port.openVirtualPort(name)
    port.ignoreTypes(false, ignoreTiming, false)
    return port
  } else {
    var count = port.getPortCount()
    for (var i=0;i < count;i++){
      if (port.getPortName(i) === name){
        if (index){
          index -= 1
        } else {
          port.openPort(i);
          port.ignoreTypes(false, ignoreTiming, false)
          return port;
        }
      }
    }
  }
  return null;
}

function getOutput(name, opts){
  if (typeof opts === 'number') opts = {index: opts}
  var index = opts && opts.index || 0
  var port = new midi.output();
  if (opts && opts.virtual){
    port.openVirtualPort(name)
    return port
  } else {
    var count = port.getPortCount()
    for (var i=0;i < count;i++){
      if (port.getPortName(i) === name){
        if (index){
          index -= 1
        } else {
          port.openPort(i);
          return port;
        }
      }
    }
  }

  return null;
}

function normalizeNotes(data) {
  if (data[0] >= 128 && data[0] < 128 + 16){
    // convert note off events to 0 velocity note on events
    data = [data[0]+16, data[1], 0]
  }
  return data
}