1. 确认项目使用的是 AudioKit 5.3.0 版本：

pod 'AudioKit', '~> 5.3.0'

2. 在 MIDICallbackInstrument 中添加回调函数：

let callbackInst = MIDICallbackInstrument()

callbackInst.setMIDIReceiver { (packetList: UnsafePointer) in
    
    var packet = packetList.pointee.packet
    
    for _ in 0 ..< packetList.pointee.numPackets {
        
        let status = packet.data.0 >> 4
        let cmd = packet.data.0 & 0xF
        let channel = packet.data.0 & 0x0F
        let data1 = packet.data.1
        let data2 = packet.data.2
        
        // your custom MIDI code goes here
        
        packet = MIDIPacketNext(&packet).pointee
    }
}

midi.addOutput(callbackInst.midiIn)

3. 在需要发送 MIDI 数据的地方准备好数据并发送：

let status = UInt8(0x90) // note on
let note = UInt8(60) // middle C
let velocity = UInt8(127)

let packet: [UInt8] = [status, note, velocity]

let packetList = UnsafeMutablePointer.allocate(capacity: 1)
var packetListPtr: UnsafeMutablePointer = MIDIPacketListInit(packetList)

packetListPtr = MIDIPacketListAdd(packetList, 1024, packetListPtr, 0, packet.count, packet)

midi.send(packetList, toDestination: midi.destinationNames[0])

4. 运行代码并测试 MIDICallbackInstrument 是否正常工作。