为什么此Web MIDI API代码无法检测MIDI事件？

Question

我正在写一个Chrome应用程序，使用当前稳定版本的Chrome (42.0.2311.152)。我在Linux和我的Chromebook上都遇到了这个问题。

我有一个可以识别的USB MIDI键盘，但没有检测到MIDI事件。我已经检查过其他程序，并确定我的设备正在发送MIDI事件。

下面是我的代码：

function midihandler( event ) {
  console.log("Received MIDI event");
  var msg = "Recieved MIDI event ";
  for (i=0 ; i < event.data.length ; i++) {
    msg += "0x" + event.data[i].toString(16) + " ";
  } 
  console.log(msg);
}

function setupMIDI() {
  navigator.requestMIDIAccess().then(
    function (m) {
       console.log("MIDI initialized");
       m.inputs.forEach(
         function (entry) {
          console.log("detected MIDI input device " + entry.name);
          entry.onmidimessage = midihandler;
          for (var key in entry) {
            console.log("entry." + key + " = " + entry[key]);
          }
        }
      );
    },
    function (msg) { console.log("error initializing MIDI: " + msg); }
    );
}


window.onload = function() {
  console.log("window.onload called");
  setupMIDI();
};

我得到的控制台输出是：

window.onload called
MIDI initialized
detected MIDI input device MPKmini2 MIDI 1
entry.onmidimessage = function midihandler( event ) {
  console.log("Received MIDI event");
  var msg = "Recieved MIDI event ";
  for (i=0 ; i < event.data.length ; i++) {
    msg += "0x" + event.data[i].toString(16) + " ";
  }
  console.log(msg);
}
entry.ondisconnect = null
entry.version = USB-Audio / ALSA library version 1.0.25
entry.type = input
entry.name = MPKmini2 MIDI 1
entry.manufacturer = AKAI
entry.id = 24:0 MPKmini2 MIDI 1
entry.addEventListener = function addEventListener() { [native code] }
entry.removeEventListener = function removeEventListener() { [native code] }
entry.dispatchEvent = function dispatchEvent() { [native code] }
detected MIDI input device Midi Through Port-0
entry.onmidimessage = function midihandler( event ) {
  console.log("Received MIDI event");
  var msg = "Recieved MIDI event ";
  for (i=0 ; i < event.data.length ; i++) {
    msg += "0x" + event.data[i].toString(16) + " ";
  }
  console.log(msg);
}
entry.ondisconnect = null
entry.version = ALSA library version 1.0.25
entry.type = input
entry.name = Midi Through Port-0
entry.manufacturer = 
entry.id = 14:0 Midi Through Port-0
entry.addEventListener = function addEventListener() { [native code] }
entry.removeEventListener = function removeEventListener() { [native code] }
entry.dispatchEvent = function dispatchEvent() { [native code] }

也就是说，设备被识别，并且onmidimessage处理程序似乎已设置。

但是，当我按下MIDI键盘上的键时，没有检测到任何事件。

我做错了什么？

Answer 1

据http://caniuse.com/#feat=midi称，Chrome43增加了对MIDI的支持。要让web MIDI在旧版本的chrome中工作，你需要在chrome设置中启用它作为一个“实验功能”，并且你需要安装jazz插件http://jazz-soft.net/doc/Jazz-Plugin/。

我已经经历了让“实验性”MIDI在我的电脑上工作的困难，但在你的情况下，更新浏览器可能是最简单的。