如何在 AudioKit 中渲染和导出音频？

Posted 2023-02-25

【中文标题】如何在 AudioKit 中渲染和导出音频？

【英文标题】：How to render and export audios in AudioKit?

【发布时间】：2018-08-24 21:51:55

【问题描述】：

我正在构建一个关于音乐的项目，并且正在使用 AudioKit 框架。 AudioKit 非常有用，但我现在需要导出应用中创建的声音。

我正在使用 AKSequencer 来按顺序播放音符，并且我还在声音上应用了一些过滤器，例如混响。

我找到了一个示例代码here，它可以从另一个音频文件中导出音频，但这不是我需要的。实际上，我需要渲染笔记序列，包括过滤器，并将其导出给用户。

我的代码：

class Sequencer 

    let oscBank = AKOscillatorBank(waveform: AKTable(AKTableType.positiveReverseSawtooth))//1
    let sequencer = AKSequencer()

    init() 
        setup()
    

    func setup() 

        // I instantiate a MIDI node with the oscillator bank to put it in the track output.
        // It makes the oscillator's filters are recognized in the track output.
        let midiNode = AKMIDINode(node: oscBank)
        _ = sequencer.newTrack()
        sequencer.tracks[0].setMIDIOutput(midiNode.midiIn)

        generateSequence()

        // Here I'm applying some filter, a reverb in this case.
        let reverb = AKReverb(oscBank)
        reverb.loadFactoryPreset(.plate)

        // The Audiokit's output may be the last filter applyed. It is working to play.
        AudioKit.output = AKMixer(reverb)
        try? AudioKit.start()
    

    func play() 
        sequencer.play()
    

    func stop() 
        sequencer.stop()
    


    /// Generates some melody (Sweet Child of Mine)
    func generateSequence() 
        for _ in 0..<2 
            sequencer.tracks[0].add(noteNumber: 62, velocity: 127, position: AKDuration(beats: 0), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 74, velocity: 127, position: AKDuration(beats: 0.5), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 69, velocity: 127, position: AKDuration(beats: 1), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 67, velocity: 127, position: AKDuration(beats: 1.5), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 79, velocity: 127, position: AKDuration(beats: 2), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 69, velocity: 127, position: AKDuration(beats: 2.5), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 78, velocity: 127, position: AKDuration(beats: 3), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 69, velocity: 127, position: AKDuration(beats: 3.5), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 62, velocity: 127, position: AKDuration(beats: 4), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 74, velocity: 127, position: AKDuration(beats: 4.5), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 69, velocity: 127, position: AKDuration(beats: 5), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 67, velocity: 127, position: AKDuration(beats: 5.5), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 79, velocity: 127, position: AKDuration(beats: 6), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 69, velocity: 127, position: AKDuration(beats: 6.5), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 78, velocity: 127, position: AKDuration(beats: 7), duration: AKDuration(beats: 0.5))
            sequencer.tracks[0].add(noteNumber: 69, velocity: 127, position: AKDuration(beats: 7.5), duration: AKDuration(beats: 0.5))
        
    


    // Here is my problem. I want to get the song and export it with the .wav extension exactly as it was played.
    // This code is just one of my many attempts and it also does not works.
    func saveFile() 
        guard let auxiliarPlayer = try? AKAudioPlayer(file: AKAudioFile(readFileName: "bass.wav")) else  return 
        guard let outputURL = try? FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false).appendingPathComponent("audio_file.m4a") else  return 
        guard let output = try? AKAudioFile(forWriting: outputURL, settings: auxiliarPlayer.audioFile.fileFormat.settings) else  return 

        try? AudioKit.renderToFile(output, seconds: sequencer.tracks[0].length, prerender: 
            self.sequencer.play()
        )
    

有人可以帮忙吗？

【参考方案1】：

据我所知，由于时间问题，离线渲染不适用于 MIDI。基本上，只能渲染处理音频的东西，而不是依赖 MIDI 的东西。我相信这与 MIDI 时钟保持不变有关，并且无法虚拟地“加速”以匹配音频渲染速度。

【讨论】：

Aurelius，你建议我们怎么做？这个功能在我们的项目中是必不可少的。

您有什么建议吗？

有人必须创建一个基于音频样本而不是 midi 时间戳的音序器才能工作。

这个问题还没有解决吗？我们也需要在我们的项目中离线渲染 MIDI 序列。