How to trigger events or callback at a specific point in an Audio Track?

Question

I want to play an Audio file (A wav file for example) and at specific locations of the track I want to fire events or triggers that will control an external device.

My idea for now is to generate a MIDI track that plays in sync with the Audio Track and when the MIDI track notes are played, some trigger events are generated that we can handle to do whatever we want.

The thing where I am stuck right now is how to play the .mid file and generate events when midi notes are played. I also want to play the wav and the mid file in sync, but that is not what I am solving at this point.

I looked into AudioKit, but the examples seem out of date and the documentation isn't helping a lot.

Is MIDI a right approach to do this? is there an easier way in iOS where I don't have to use AudioKit and just use something from AVFoundation.

I want to understand what tool is best to detect when a midi note from the .mid file is played and handle the event.

My research has pointed me to use AKAppleSequencer. What could help is a simple example that loads a midi file and then basically prints something when a note is played.

I came across these posts,

How to connect AKSequencer to a AKCallbackInstrument?

Play MIDI file together with wav AudioKit

but the AKSequencer is now replaced by AKAppleSequencer.

Answer 1

So I figured it out. The answer was basically in the posts above just updated the code so it uses AKAppleSequencer.

let sequencer = AKAppleSequencer(filename: "SaReGaMa") // the .mid file
let callbackInstr = AKMIDICallbackInstrument()
var player: AKPlayer!

func initializeSession() {
        callbackInstr.callback = myCallBack
        sequencer.setGlobalMIDIOutput(callbackInstr.midiIn)
        if let audioFile = try? AKAudioFile(readFileName: "SaReGaMa.wav") {
            player = AKPlayer(audioFile: audioFile)
            player.completionHandler = { print("Finished playing file")}
            player.buffering = .always

            AudioKit.output = player
            do {
                try AudioKit.start()

            } catch {
                print("Error starting audiokit, \(error)")
            }
        }
}

// The callback gets triggered when each midi note is played by the sequencer.
func myCallBack(a: UInt8, b:MIDINoteNumber, c:MIDIVelocity) -> () {
        print(a,b,c);
}

// These functions let you control the playback. 
func play() {
        player.play()
        sequencer.play()
}

func pause() {
        sequencer.stop()
        player.pause()
}