AudioKit ios AKSequencer 无法准确重启播放

Question

我正在尝试使用 AudioKit 在小节的每个节拍上播放声音。虽然我已经通过 AudioKit 实现了 similar question regarding callbacks 中的代码，但我似乎无法让音序器正确更新更改和播放。它会准确播放一次，但是在倒带和更改值后它只会使用初始值（或根本不播放）。

我的目的是为每个小节创建一个带有节拍值的小节结构，然后使用 MIDI 和回调来播放不同的声音，具体取决于有多少 measures/beats。谢谢！

import UIKit
import AudioKit

class ViewController: UIViewController {

let sequencer = AKSequencer()

let click = AKSynthSnare()
let callbackInst = AKCallbackInstrument()

// Create the struct that defines each line
struct Line {
    var name: String
    var measures: Int
    var beatsPerMeasure: Int
    func totalBeats() -> Int {
        return (measures * beatsPerMeasure)
    }
}

// Initialize intro line
var intro = Line(name: "Intro", measures: 0, beatsPerMeasure: 0)

// A function to create/update/playback the sequence on button press
func playBack() {

    let metronomeTrack = sequencer.newTrack()
    metronomeTrack?.setMIDIOutput(click.midiIn)
    let callbackTrack = sequencer.newTrack()
    callbackTrack?.setMIDIOutput(callbackInst.midiIn)

    for steps in 0 ... Int(measuresRowOneValue) {
        // this will trigger the sampler on the four down beats
        metronomeTrack?.add(noteNumber: 60, velocity: 100, position: AKDuration(beats: Double(steps)), duration: AKDuration(beats: 0.5))

        // set the midiNote number to the current beat number
        callbackTrack?.add(noteNumber: MIDINoteNumber(steps), velocity: 100, position: AKDuration(beats: Double(steps)), duration: AKDuration(beats: 0.5))

        // set the callback
        callbackInst.callback = {status, noteNumber, velocity in
            guard status == .noteOn else { return }
            print("beat number: \(noteNumber + 1)")

        }
    }
}


@IBOutlet weak var rowOneLocationOne: UIImageView!
// Listener for UI display values
var measuresRowOneValue: Int = 0 {
    didSet {
        intro.measures = measuresRowOneValue
    }
}

@IBAction func rowOnePlusButton(_ sender: UIButton) {
    measuresRowOneValue += 1
}

@IBAction func rowOneMinusButton(_ sender: UIButton) {
    measuresRowOneValue -= 1
}

@IBAction func playbackStart(_ sender: UIButton) {
    playBack()
    sequencer.play()
}

@IBAction func playbackStop(_ sender: UIButton) {
    sequencer.stop()
}

@IBAction func playbackRestart(_ sender: UIButton) {
    sequencer.rewind()
}

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    AudioKit.output = click
    try!AudioKit.start()
}
}

Answer 1

你的代码中有一些令人困惑的地方，所以我不确定这是否是你唯一的问题，但至少，每次你改变序列的长度时，你都需要调用 setLength() 后跟 enableLooping。基本上，默认情况下（即，除非您明确设置长度）序列的长度将是序列中最长轨道的长度。在您的 'playback' 方法中，您是在不删除旧轨道的情况下在轨道之上添加轨道，因此它无法知道您希望序列持续多长时间。

您的 'playback' 方法正在做两件不同的事情（两者都不涉及回放）。你可能想打破它。你可以有一个 setup() 来做那些只需要做一次的事情（创建音轨，设置它们的输出，设置回调）和一个 rewriteSequence() 方法，当你想要的时候被调用重写曲目。这样您就可以重复使用现有曲目，而不是不断创建新曲目。

var metronomeTrack: AKMusicTrack!
var callbackTrack: AKMusicTrack!

    // call this just once at the start
    func setup() {
        metronomeTrack = sequencer.newTrack()
        metronomeTrack?.setMIDIOutput(click.midiIn)
        callbackTrack = sequencer.newTrack()
        callbackTrack?.setMIDIOutput(callbackInst.midiIn)

        callbackInst.callback = {status, noteNumber, velocity in
            guard status == .noteOn else { return }
            print("beat number: \(noteNumber + 1)")

        }
    }

    // call this each time you want to change the sequence
    func rewriteSequence() {
        metronomeTrack?.clear()
        callbackTrack?.clear()
        for steps in 0 ... Int(measuresRowOneValue) {
            metronomeTrack?.add(noteNumber: 60, velocity: 100, position: AKDuration(beats: Double(steps)), duration: AKDuration(beats: 0.5))
            callbackTrack?.add(noteNumber: MIDINoteNumber(steps), velocity: 100, position: AKDuration(beats: Double(steps)), duration: AKDuration(beats: 0.5))
        }

        // This will make sure it loops correctly:
        sequencer.setLength(AKDuration(beats: Double(measuresRowOneValue)))
        sequencer.enableLooping()
    }

希望对您有所帮助。

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