如何改变录制音频的音高让我跟随错误

Question

由于未捕获的异常'com.apple.coreaudio.avfaudio'而终止应用程序，原因：'必需条件为false：node！= nil'

AVAudioFile *file=[[AVAudioFile alloc] initForReading:_recordedvoice error:nil];
AVAudioFormat *format=file.processingFormat;
AVAudioFrameCount capacity= (AVAudioFrameCount)file.length;
AVAudioPCMBuffer *buffer=[[AVAudioPCMBuffer alloc] initWithPCMFormat:format frameCapacity:capacity];
[file readIntoBuffer:buffer error:nil];
[playerNode scheduleBuffer:buffer completionHandler:nil];

engine = [[AVAudioEngine alloc] init];
    playerNode = [[AVAudioPlayerNode alloc] init];

[engine attachNode: playerNode];

AVAudioMixerNode *mixer = engine.mainMixerNode;
AVAudioUnitTimePitch *auTimePitch;
auTimePitch.pitch=1200.0;// In cents. The default value is 1.0. The range of values is -2400 to 2400
auTimePitch.rate = 2.0; //The default value is 1.0. The range of supported values is 1/32 to 32.0.

//get the error in the following line

[engine attachNode: auTimePitch];
[engine connect:playerNode to:auTimePitch format:[mixer outputFormatForBus:0]];
[engine connect:playerNode to:mixer format:[mixer outputFormatForBus:0]];

[playerNode play];

Answer 1

在调用play之前先尝试启动引擎：

[self.engine startAndReturnError:nil];
[playerNode play];