在AVAudioEngine中不能播放AVAudioFile

Question

我正在尝试使用AVAudioEngine播放AVAudioFile。代码主要取自Apple Developer的在线视频，但没有回放功能。我花了一些时间浏览论坛，但似乎没有任何线索。

我有两个方法。第一个调用标准的打开文件对话框，打开音频文件，分配一个AVAudioBuffer对象(我稍后将使用它)，并用音频数据填充它。第二个是设置AVAudioEngine和AVAudioPlayerNode对象，连接所有内容并播放文件。下面列出了这两种方法。

- (IBAction)getSoundFileAudioData:(id)sender {


    NSOpenPanel* openPanel = [NSOpenPanel openPanel];

    openPanel.title = @"Choose a .caf file";
    openPanel.showsResizeIndicator = YES;
    openPanel.showsHiddenFiles = NO;
    openPanel.canChooseDirectories = NO;
    openPanel.canCreateDirectories = YES;
    openPanel.allowsMultipleSelection = NO;
    openPanel.allowedFileTypes = @[@"caf"];

    [openPanel beginWithCompletionHandler:^(NSInteger result){
       if (result == NSFileHandlingPanelOKButton) {
        NSURL*  theAudioFileURL = [[openPanel URLs] objectAtIndex:0];

        // Open  the document.

        theAudioFile = [[AVAudioFile alloc] initForReading:theAudioFileURL error:nil];

        AVAudioFormat *format = theAudioFile.processingFormat;
        AVAudioFrameCount capacity = (AVAudioFrameCount)theAudioFile.length;

        theAudioBuffer = [[AVAudioPCMBuffer alloc] 
             initWithPCMFormat:format frameCapacity:capacity];
        NSError *error;
        if (![theAudioFile readIntoBuffer:theAudioBuffer error:&error])  {

            NSLog(@"problem filling buffer");

        }
        else
            playOrigSoundFileButton.enabled = true;            

    }

}];}





- (IBAction)playSoundFileAudioData:(id)sender {



    AVAudioEngine *engine = [[AVAudioEngine alloc] init]; // set up the audio engine

    AVAudioPlayerNode *player = [[AVAudioPlayerNode alloc] init]; // set up a player node

    [engine attachNode:player]; // attach player node to engine

    AVAudioMixerNode *mixer = [engine mainMixerNode];
    [engine connect:player to:mixer format:theAudioFile.processingFormat]; // connect player node to mixer
    [engine connect:player to:mixer format:[mixer outputFormatForBus:0]]; // connect player node to mixer

    NSError *error;

    if (![engine startAndReturnError:&error]) {
        NSLog(@"Problem starting engine ");
    }
    else {

        [player scheduleFile:theAudioFile atTime: nil completionHandler:nil];
        [player play];
    }

}

我已经检查了函数是否正在执行、音频引擎是否正在运行以及音频文件是否已被读取。我还尝试了不同的音频文件格式，包括单声道和立体声。有什么想法吗？

我运行的是Xcode 7.3.1。