尝试以样本缓冲区作为输入设置音频单元图

我正在尝试实现一个简单的音频单元图,该图可以:

样本缓冲区->低通滤波器->通用输出

将通用输出复制到新的缓冲区,然后可以进一步处理,保存到磁盘等。

我可以在网上找到的所有与设置音频单元图有关的示例都涉及使用具有kAudioUnitSubType_AudioFilePlayer作为输入源的生成器。。。我正在处理一个已经获取的样本缓冲区,因此这些示例没有帮助。。。根据AudioUnitProperties.h文件中的查找,我应该使用的是kAudioUnitSubType_ScheduledSoundPlayer?

我似乎没有太多关于如何连接这个的文档,所以我很困,希望这里的人能帮我。

为了简化事情,我刚开始尝试让我的样本缓冲区直接进入系统输出,但我无法做到这一点。。。

  #import "EffectMachine.h"
  #import <AudioToolbox/AudioToolbox.h>
  #import "AudioHelpers.h"
  #import "Buffer.h"

  @interface EffectMachine ()
  @property (nonatomic, strong) Buffer *buffer;
  @end

  typedef struct EffectMachineGraph {
      AUGraph   graph;
      AudioUnit input;
      AudioUnit lowpass;
      AudioUnit output;
  } EffectMachineGraph;

  @implementation EffectMachine {
      EffectMachineGraph machine;
  }

  -(instancetype)initWithBuffer:(Buffer *)buffer {
      if (self = [super init]) {
          self.buffer = buffer;

          // buffer is a simple wrapper object that holds two properties:
          // a pointer to the array of samples (as doubles) and the size (number of samples)

      }
      return self;
  }

  -(void)process {
      struct EffectMachineGraph initialized = {0};
      machine = initialized;

      CheckError(NewAUGraph(&machine.graph),
                 "NewAUGraph failed");

      AudioComponentDescription outputCD = {0};
      outputCD.componentType = kAudioUnitType_Output;
      outputCD.componentSubType = kAudioUnitSubType_DefaultOutput;
      outputCD.componentManufacturer = kAudioUnitManufacturer_Apple;

      AUNode outputNode;
      CheckError(AUGraphAddNode(machine.graph,
                                &outputCD,
                                &outputNode),
                 "AUGraphAddNode[kAudioUnitSubType_GenericOutput] failed");

      AudioComponentDescription inputCD = {0};
      inputCD.componentType = kAudioUnitType_Generator;
      inputCD.componentSubType = kAudioUnitSubType_ScheduledSoundPlayer;
      inputCD.componentManufacturer = kAudioUnitManufacturer_Apple;

      AUNode inputNode;
      CheckError(AUGraphAddNode(machine.graph,
                                &inputCD,
                                &inputNode),
                 "AUGraphAddNode[kAudioUnitSubType_ScheduledSoundPlayer] failed");

      CheckError(AUGraphOpen(machine.graph),
                 "AUGraphOpen failed");

      CheckError(AUGraphNodeInfo(machine.graph,
                                 inputNode,
                                 NULL,
                                 &machine.input),
                 "AUGraphNodeInfo failed");

      CheckError(AUGraphConnectNodeInput(machine.graph,
                                         inputNode,
                                         0,
                                         outputNode,
                                         0),
                 "AUGraphConnectNodeInput");

      CheckError(AUGraphInitialize(machine.graph),
                 "AUGraphInitialize failed");

      // prepare input

      AudioBufferList ioData = {0};
      ioData.mNumberBuffers = 1;
      ioData.mBuffers[0].mNumberChannels = 1;
      ioData.mBuffers[0].mDataByteSize = (UInt32)(2 * self.buffer.size);
      ioData.mBuffers[0].mData = self.buffer.samples;

      ScheduledAudioSlice slice = {0};
      AudioTimeStamp timeStamp  = {0};

      slice.mTimeStamp    = timeStamp;
      slice.mNumberFrames = (UInt32)self.buffer.size;
      slice.mBufferList   = &ioData;

      CheckError(AudioUnitSetProperty(machine.input,
                                      kAudioUnitProperty_ScheduleAudioSlice,
                                      kAudioUnitScope_Global,
                                      0,
                                      &slice,
                                      sizeof(slice)),
                 "AudioUnitSetProperty[kAudioUnitProperty_ScheduleStartTimeStamp] failed");

      AudioTimeStamp startTimeStamp = {0};
      startTimeStamp.mFlags = kAudioTimeStampSampleTimeValid;
      startTimeStamp.mSampleTime = -1;

      CheckError(AudioUnitSetProperty(machine.input,
                                      kAudioUnitProperty_ScheduleStartTimeStamp,
                                      kAudioUnitScope_Global,
                                      0,
                                      &startTimeStamp,
                                      sizeof(startTimeStamp)),
                 "AudioUnitSetProperty[kAudioUnitProperty_ScheduleStartTimeStamp] failed");

      CheckError(AUGraphStart(machine.graph),
                 "AUGraphStart failed");

  //    AUGraphStop(machine.graph);  <-- commented out to make sure it wasn't stopping before actually finishing playing.
  //    AUGraphUninitialize(machine.graph);
  //    AUGraphClose(machine.graph);

  }

有人知道我在这里做错了什么吗?