如何用AudioKit Sequencer在指定位置播放本地音频文件？

Alright, let's get this sorted! The key here is to swap out the default AKSynthSnare with AKPlayer instances (one for your high-frequency audio, one for low) and map each character in your binary string to a timed event in the AudioKit Sequencer. Here's how to do it step by step:

Step 1: Prepare Your Audio Players #

First, we'll create two AKPlayer objects to handle your local high and low frequency audio files. These players will be triggered by the sequencer at the correct positions.

import AudioKit

class AudioSequencePlayer {
    // Core audio setup
    let engine = AudioEngine()
    let mixer = Mixer()
    
    // Players for high/low frequency sounds
    var highFreqPlayer: AKPlayer!
    var lowFreqPlayer: AKPlayer!
    
    // Sequencer and track to handle timing
    var sequencer: Sequencer!
    var track: Track!
    
    init() {
        // Load local audio files - replace with your actual file names/extensions
        guard let highFreqURL = Bundle.main.url(forResource: "high_tone", withExtension: "wav"),
              let lowFreqURL = Bundle.main.url(forResource: "low_tone", withExtension: "wav") else {
            fatalError("Couldn't locate audio files in the app bundle!")
        }
        
        // Initialize players and configure for single-shot playback
        highFreqPlayer = AKPlayer(url: highFreqURL)
        lowFreqPlayer = AKPlayer(url: lowFreqURL)
        
        highFreqPlayer.isLooping = false
        lowFreqPlayer.isLooping = false
        
        // Route audio flow: players → mixer → engine output
        highFreqPlayer >>> mixer
        lowFreqPlayer >>> mixer
        engine.output = mixer
    }
}

Step 2: Map Binary String to Sequencer Timed Events #

Next, we'll add a method to parse your binary string, iterate over each character, and place trigger events at the exact beat positions using AKDuration(beats:).

Add this method inside the AudioSequencePlayer class:

func setupSequence(with binaryString: String) {
    // Reset sequencer and track
    sequencer = Sequencer()
    track = sequencer.addTrack()
    track.clear()
    
    // Loop through each character in the binary input
    for (index, char) in binaryString.enumerated() {
        // Calculate position: each character corresponds to 1 beat
        let eventPosition = AKDuration(beats: Double(index))
        
        // Assign unique MIDI note numbers to distinguish high/low triggers
        let triggerNote: MIDINoteNumber = char == "1" ? 60 : 40
        
        // Add the note event to the track (short duration to avoid hanging notes)
        track.add(triggerNote, velocity: 127, position: eventPosition, duration: AKDuration(beats: 0.4))
    }
    
    // Attach a listener to catch MIDI events and trigger the right player
    sequencer.addMIDIListener(self)
}

Step 3: Trigger Players via MIDI Events #

We need to conform to AKMIDIListener to respond to the sequencer's note events and play the corresponding audio file. Add this extension:

extension AudioSequencePlayer: AKMIDIListener {
    func receivedMIDINoteOn(noteNumber: MIDINoteNumber, velocity: MIDIVelocity, channel: MIDIChannel) {
        // Trigger the correct player based on our assigned note numbers
        if noteNumber == 60 {
            // Reset and play high frequency sound (ensures it starts from the top)
            highFreqPlayer.stop()
            highFreqPlayer.play()
        } else if noteNumber == 40 {
            lowFreqPlayer.stop()
            lowFreqPlayer.play()
        }
    }
}

Step 4: Control Sequence Playback #

Add these helper methods to start/stop the sequence and manage the audio engine:

func startSequence() {
    do {
        try engine.start()
        sequencer.play()
    } catch {
        print("Failed to start audio engine: \(error.localizedDescription)")
    }
}

func stopSequence() {
    sequencer.stop()
    engine.stop()
    highFreqPlayer.stop()
    lowFreqPlayer.stop()
}

How to Use the Class #

Initialize and trigger your sequence with a binary string like this:

let audioPlayer = AudioSequencePlayer()
audioPlayer.setupSequence(with: "1100011010")
audioPlayer.startSequence()

// To stop playback later:
// audioPlayer.stopSequence()

Quick Tips #

• Replace "high_tone.wav" and "low_tone.wav" with your actual local audio file names and extensions (supports most common formats like MP3, WAV).
• Adjust the duration parameter in track.add() if you need longer/shorter playback of each sound.
• The stop() call before play() ensures the audio file restarts from the beginning every time it's triggered, even if it was already playing.

内容的提问来源于stack exchange，提问作者Jonas0000