如何用AudioKit的MIDIPlayer播放MIDI文件？报错-10852求解

问题重现 #

使用AudioKit的MIDIPlayer播放MIDI文件，编写了如下SwiftUI代码：

import SwiftUI
import AudioKit

struct ContentView: View {
    @StateObject var midi = MIDIWrapper()
    
    var body: some View {
        Button(action: {midi.play()}, label: {Text("play")})     
    }
}

class MIDIWrapper: ObservableObject {
    
    let engine = AudioEngine()
    var instrument = AppleSampler()
    let player: MIDIPlayer
    
    init() {
        engine.output = instrument
        
        try? engine.start()
        
        player = MIDIPlayer(audioEngine: engine.avEngine, filename: "cdec.mid")
    }
    
    func play() -> () {
        player.play()
    }  
}

在iPhone 13上运行时出现以下错误：

AVAEInternal.h:109   [AVAudioSequencer.mm:121:-[AVAudioSequencer(AVAudioSequencer_Player) startAndReturnError:]: (impl->Start()): error -10852
MIDIPlayer.swift:play():121:Could not start the sequencer (MIDIPlayer.swift:play():121)

解决方法 #

1. 配置正确的音频会话 #

iOS要求音频应用必须提前配置AVAudioSession，获取音频权限并设置合适的播放类别。在MIDIWrapper初始化中添加会话配置：

import SwiftUI
import AudioKit
import AVFoundation // 需导入AVFoundation

class MIDIWrapper: ObservableObject {
    
    let engine = AudioEngine()
    var instrument = AppleSampler()
    let player: MIDIPlayer
    
    init() {
        // 配置音频会话
        do {
            let session = AVAudioSession.sharedInstance()
            try session.setCategory(.playback, mode: .default)
            try session.activate()
        } catch {
            print("音频会话配置失败: \(error)")
        }
        
        engine.output = instrument
        
        // 捕获AudioEngine启动错误
        do {
            try engine.start()
        } catch {
            print("AudioEngine启动失败: \(error)")
        }
        
        player = MIDIPlayer(audioEngine: engine.avEngine, filename: "cdec.mid")
    }
    
    func play() {
        player.play()
    }  
}

2. 验证MIDI文件的项目配置 #

• 确认cdec.mid已添加到Xcode项目的目标中：选中文件，查看右侧检查器的Target Membership，确保勾选当前应用目标。
• 检查文件名拼写完全一致：iOS区分文件名大小写，代码中的"cdec.mid"必须和实际文件名完全匹配。

3. 确保MIDIPlayer加载完成后再调用播放 #

MIDI文件加载需要时间，可通过异步加载或状态检查避免未初始化完成就调用play：

class MIDIWrapper: ObservableObject {
    
    let engine = AudioEngine()
    var instrument = AppleSampler()
    var player: MIDIPlayer?
    
    init() {
        // 配置音频会话...
        
        engine.output = instrument
        
        do {
            try engine.start()
            // 异步加载MIDI文件
            DispatchQueue.global().async { [weak self] in
                guard let self = self else { return }
                self.player = MIDIPlayer(audioEngine: self.engine.avEngine, filename: "cdec.mid")
                self.player?.load() // 显式触发加载
            }
        } catch {
            print("AudioEngine启动失败: \(error)")
        }
    }
    
    func play() {
        guard let player = player else {
            print("MIDIPlayer未完成初始化")
            return
        }
        player.play()
    }  
}

4. 替换静默错误捕获为显式异常处理 #

原代码中try? engine.start()会忽略错误，改为do-catch可以获取具体失败原因，帮助排查问题：

do {
    try engine.start()
} catch {
    print("AudioEngine启动失败详情: \(error.localizedDescription)")
}

内容的提问来源于stack exchange，提问作者Jesse