AVAudiounit:我不能播放像延迟这样的声音效果

Question

我是objective c的新手，并尝试编写一个可以播放声音并对其产生影响的程序，比如混响或延迟。不幸的是，我只能播放声音，但没有效果。我被困了3天，找不到解决办法。有谁能说出我做错了什么吗？我试过这段代码，但它根本没有声音：

- (void)viewDidLoad {
    [super viewDidLoad];
    AVAudioEngine *engine = [AVAudioEngine new];
    AVAudioPlayerNode *playerA = [AVAudioPlayerNode new];

    playerA.volume = 0.5;


    NSURL *Mia1url = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"MIA1" ofType:@"m4a"]];

    AVAudioFile *MIA1 = [[AVAudioFile alloc] initForReading:Mia1url error:nil];
    AVAudioPCMBuffer *buffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:MIA1.processingFormat frameCapacity:1024];
    [MIA1 readIntoBuffer:buffer error:nil];

    AVAudioUnitDelay *delay = [AVAudioUnitDelay new];
    delay.delayTime = 100;
    delay.wetDryMix = 90;

    [engine attachNode:playerA];
    [engine attachNode:delay];

    [engine connect: playerA to: delay format:MIA1.processingFormat];
    [engine connect: delay to: engine.mainMixerNode format: MIA1.processingFormat];

    [playerA scheduleBuffer:buffer atTime:nil options:AVAudioPlayerNodeBufferLoops completionHandler:nil];

    [engine prepare];
    [engine startAndReturnError:nil];

    [playerA play];
}

在那之后，我尝试了这个代码，但是声音是没有效果的：

- (void)viewDidLoad {
    [super viewDidLoad];
    AVAudioEngine *engine = [AVAudioEngine new];
    AVAudioPlayerNode *playerA = [AVAudioPlayerNode new];

    playerA.volume = 0.5;

    NSURL *Mia1url = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"MIA1" ofType:@"m4a"]];

    AVAudioFile *MIA1 = [[AVAudioFile alloc] initForReading:Mia1url error:nil];
    AVAudioPCMBuffer *buffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:MIA1.processingFormat frameCapacity:1024];
    [MIA1 readIntoBuffer:buffer error:nil];

    AVAudioUnitDelay *delay = [AVAudioUnitDelay new];
    delay.delayTime = 100;
    delay.wetDryMix = 90;

    [engine attachNode:playerA];
    [engine attachNode:delay];

    [engine connect: playerA to: delay format:MIA1.processingFormat];
    [engine connect: delay to: engine.mainMixerNode format: MIA1.processingFormat];

    [playerA scheduleBuffer:buffer atTime:nil options:AVAudioPlayerNodeBufferLoops completionHandler:nil];

    [engine prepare];
    [engine startAndReturnError:nil];

    //change
    self.playerA = [[AVAudioPlayer alloc] initWithContentsOfURL:Mia1url error:nil];

    //change from [playerA play] to:
    [self.playerA play];
}

Answer 1

你忘了实例化你的对象：

//AVAudioEngine *engine; // no instance exists. 
AVAudioEngine *engine = [AVAudioEngine new]; 
AVAudioPlayerNode *playerA = [AVAudioPlayerNode new];

...

AVAudioUnitDelay *delay = [AVAudioUnitDelay new];
...

此外，在使用playerA之前，您只需初始化它一次。

为了更深入地挖掘，您可能想要检查Apples code samples。