how to change the pitch of recorded audio getting me following error

问题

Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is 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];

回答1:

Try starting the engine first before calling play:

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

来源：https://stackoverflow.com/questions/38634069/how-to-change-the-pitch-of-recorded-audio-getting-me-following-error