如何在播放过程中改变音频音调？（Swift 4）

Question

我希望能够使用滑块或变量（即在声音播放时）实时更改Xcode，Swift 4中的某些音频的音高和播放速度。

目前，我正在使用AVAudioEngine，在播放开始之前可以设置这些值，但是我无法在音频实际播放时更改它们。

以下是相关代码：

func Play() {
    engine = AVAudioEngine()
    audioPlayer = AVAudioPlayerNode()
    audioPlayer.volume = 1.0

    let path = Bundle.main.path(forResource: "filename", ofType: "mp3")!
    let url = NSURL.fileURL(withPath: path)

    let file = try? AVAudioFile(forReading: url)
    let buffer = AVAudioPCMBuffer(pcmFormat: file!.processingFormat, frameCapacity: AVAudioFrameCount(file!.length))
    do {
        try file!.read(into: buffer!)
    } catch _ {
    }

    let pitch = AVAudioUnitTimePitch()
    let speed = AVAudioUnitVarispeed()

    pitch.pitch = speedIncrement * (-500)
    speed.rate = speedIncrement

    engine.attach(audioPlayer)

    engine.attach(pitch)

    engine.attach(speed)

    engine.connect(audioPlayer, to: speed, format: buffer?.format)

    engine.connect(speed, to: pitch, format: buffer?.format)

    engine.connect(pitch, to: engine.mainMixerNode, format: buffer?.format)

    audioPlayer.scheduleBuffer(buffer!, at: nil, options: AVAudioPlayerNodeBufferOptions.loops, completionHandler: nil)

    engine.prepare()
    do {
        try engine.start()
    } catch _ {
    }

    audioPlayer.play()

}

AVAudioEngine能否实现这一点？

如果AVAudioEngine无法实现这一点，还有哪些可能的解决方案？

- will

Answer 1

实际上，我从Reddit上得到了答案。我所要做的就是在Play()函数之外声明pitch和speed变量，以及pitch.pitch = speedIncrement * (-500)和speed.rate = speedIncrement表达式。我知道我错过了一些简单的东西...

- will

Answer 2

你要做的事情在这个链接中得到了解决: https://www.hackingwithswift.com/example-code/media/how-to-control-the-pitch-and-speed-of-audio-using-avaudioengine。我使用它并且可以正常工作。我注意到音高和速度变化很敏感。我将我的设置为:

pitch.pitch -= 0.2
speed.rate -= 0.2

- Andrew