objective-c - 将 AVAudioUnitEffect 与 AVAudioEngine 连接时遇到问题

Question

我一直在研究 AVAudioEngine，但在集成 AVAudioUnitEffect 类时遇到了问题。例如，使用 AVAudioUnitDelay...

@implementation ViewController {
AVAudioEngine *engine;
AVAudioPlayerNode *player;
}

...

- (IBAction)playButtonHit:(id)sender {
if (!player){
    NSURL *bandsURL = [[NSBundle mainBundle] URLForResource:@"Bands With Managers" withExtension:@"mp3"];
    AVAudioFile *file = [[AVAudioFile alloc] initForReading:bandsURL error:nil];

    engine = [[AVAudioEngine alloc] init];
    player = [[AVAudioPlayerNode alloc] init];
    [engine attachNode:player];

    AVAudioUnitDelay *delay = [[AVAudioUnitDelay alloc] init];
    delay.wetDryMix = 50;

    [engine connect:player to:delay format:file.processingFormat];
    [engine connect:delay to:[engine outputNode] format:file.processingFormat];

    [player scheduleFile:file atTime:nil completionHandler:nil];
    [engine prepare];
    [engine startAndReturnError:nil];
}
[player play];  

}

当调用该方法时，应用程序崩溃，我收到此错误:“* 由于未捕获的异常“com.apple.coreaudio.avfaudio”而终止应用程序，原因:“所需条件为假: [_nodes containsObject:node1] && [_nodes containsObject:node2]'"

我根据 WWDC 的“AVAudioEngine 实践” session 中的一些示例对此进行建模。我知道我可能遗漏了一些明显的东西，但无法弄清楚......

Answer 1

在链接它们之前，您忘记将 AvAudioUnitDelay 对象附加到 AvAudioEngine 节点；)

这是工作代码:

- (IBAction)playMusic:(id)sender {
    if (!player){
        NSURL *bandsURL = [[NSBundle mainBundle] URLForResource:@"Bands With Managers" withExtension:@"mp3"];
        AVAudioFile *file = [[AVAudioFile alloc] initForReading:bandsURL error:nil];

        engine = [[AVAudioEngine alloc] init];
        player = [[AVAudioPlayerNode alloc] init];
        [engine attachNode:player];

        AVAudioUnitDelay *delay = [[AVAudioUnitDelay alloc] init];
        delay.wetDryMix = 50;
        [engine attachNode:delay]; 

        [engine connect:player to:delay format:file.processingFormat];
        [engine connect:delay to:[engine outputNode] format:file.processingFormat];

        [player scheduleFile:file atTime:nil completionHandler:nil];
        [engine prepare];
        [engine startAndReturnError:nil];
    }
    [player play]; 
}