Our audio app is using AUGraphs containing a mixer unit, a converter unit and an output unit. It s a realtime app, so performance is a high concern.

有一个问题被揭开,即AUGraphStop(AU GraphStop)需要25毫秒才能在主线上完成,我们的简介员显示,它花费了这一时间睡觉。 是否有人解释为什么会发生这种情况? 是否等待下一个零交叉点,还是等待一个额外的缓冲点来做到这一点?

I ve tried several workarounds, including sending one render frame of silence (and setting the kAudioUnitRenderAction_OutputIsSilence flag) before attempting to stop, and calling AUGraphStop() inside the kAudioUnitRenderAction_PostRender notify callback (this has mixed results, and after reading around it doesn t seem a recommended approach).

我尝试降低每个胎体的大小,但似乎没有改变。 除产出节点外,我还试图拆除所有音频单位,试图将问题缩小到一个具体单位,但非洲联盟格拉斯托(AU GraphStop)的费用仍然为25米。

这里,我们是如何初步拟定图表的:

//Configure converter/mixer/output unit descriptors
AudioComponentDescription OutputUnitDesc = { kAudioUnitType_Output ,kAudioUnitSubType_DefaultOutput, kAudioUnitManufacturer_Apple };
AudioComponentDescription MixerUnitDesc = { kAudioUnitType_Mixer, kAudioUnitSubType_MatrixMixer, kAudioUnitManufacturer_Apple };
AudioComponentDescription ConverterUnitDesc = { kAudioUnitType_FormatConverter, kAudioUnitSubType_AUConverter, kAudioUnitManufacturer_Apple };

//Create graph
CA_ERR(NewAUGraph(&mAudioGraph));

//Add converter/mixer/output nodes
CA_ERR(AUGraphAddNode(mAudioGraph, &OutputUnitDesc, &mOutputNode));
CA_ERR(AUGraphAddNode(mAudioGraph, &MixerUnitDesc, &mMixerNode));
CA_ERR(AUGraphAddNode(mAudioGraph, &ConverterUnitDesc, &mConverterNode));

//Connect nodes
CA_ERR(AUGraphConnectNodeInput(mAudioGraph, mConverterNode, 0, mMixerNode, 0));
CA_ERR(AUGraphConnectNodeInput(mAudioGraph, mMixerNode, 0, mOutputNode, 0));

//Open the graph (instantiates the units)
CA_ERR(AUGraphOpen(mAudioGraph));

//Get the created units
CA_ERR(AUGraphNodeInfo(mAudioGraph, mOutputNode, NULL, &mOutputUnit));
CA_ERR(AUGraphNodeInfo(mAudioGraph, mMixerNode, NULL, &mMixerUnit));
CA_ERR(AUGraphNodeInfo(mAudioGraph, mConverterNode, NULL, &mConverterUnit));

//Setup stream format description
mStreamDesc.mFormatID = kAudioFormatLinearPCM;
mStreamDesc.mFormatFlags = kLinearPCMFormatFlagIsPacked | kAudioFormatFlagIsSignedInteger;
mStreamDesc.mChannelsPerFrame = Header->nChannels;
mStreamDesc.mSampleRate = (Float64)Header->nSamplesPerSec;
mStreamDesc.mBitsPerChannel = Header->wBitsPerSample;
mStreamDesc.mBytesPerFrame = (Header->wBitsPerSample >> 3) * Header->nChannels;
mStreamDesc.mFramesPerPacket = 1;
mStreamDesc.mBytesPerPacket = mStreamDesc.mBytesPerFrame * mStreamDesc.mFramesPerPacket;
mStreamDesc.mReserved = 0;

//Set data endianness according to file type - TODO: Get endianness from header
AudioSystem::FileType FileType = mSample->GetFiletype();

if(FileType == AudioSystem::WAV)
        mStreamDesc.mFormatFlags |= kAudioFormatFlagsNativeEndian;
else if(FileType == AudioSystem::OGG)
        mStreamDesc.mFormatFlags |= kLinearPCMFormatFlagIsBigEndian;

//Configure number of input/output busses for mixer unit
int NumChannelsIn = Header->nChannels;
int NumChannelsOut = (int)AudioSystem::GetOutputChannelConfig();
CA_ERR(AudioUnitSetProperty(mMixerUnit, kAudioUnitProperty_BusCount, kAudioUnitScope_Input, 0, &NumChannelsIn, sizeof(u32)));
CA_ERR(AudioUnitSetProperty(mMixerUnit, kAudioUnitProperty_BusCount, kAudioUnitScope_Output, 0, &NumChannelsOut, sizeof(u32)));

//Set render callback
AURenderCallbackStruct callback = { AudioRenderCallback, this };
CA_ERR(AUGraphSetNodeInputCallback(mAudioGraph, mConverterNode, 0, &callback));

//Set stream format to something native to CoreAudio
AudioStreamBasicDescription OutputDesc = {0};
UInt32 Size = sizeof(AudioStreamBasicDescription);
CA_ERR(AudioUnitGetProperty(mMixerUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &OutputDesc, &Size));

//Set num output channels
OutputDesc.mChannelsPerFrame = (int)AudioSystem::GetOutputChannelConfig();

//Set stream format
CA_ERR(AudioUnitSetProperty(mConverterUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &mStreamDesc, sizeof(AudioStreamBasicDescription)));
CA_ERR(AudioUnitSetProperty(mConverterUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, &OutputDesc, sizeof(AudioStreamBasicDescription)));
CA_ERR(AudioUnitSetProperty(mMixerUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &OutputDesc, sizeof(AudioStreamBasicDescription)));
CA_ERR(AudioUnitSetProperty(mMixerUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, &OutputDesc, sizeof(AudioStreamBasicDescription)));
CA_ERR(AudioUnitSetProperty(mOutputUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &OutputDesc, sizeof(AudioStreamBasicDescription)));

//Initialise graph
CA_ERR(AUGraphInitialize(mAudioGraph));

//Set notification callback
CA_ERR(AUGraphAddRenderNotify(mAudioGraph, AudioNotifyCallback, this));

//Set global mixer volume
CA_ERR(AudioUnitSetParameter(mMixerUnit, kMatrixMixerParam_Volume, kAudioUnitScope_Global, 0xFFFFFFFF, 1.0, 0));

//Set input channel volumes
for(int i = 0; i < Header->nChannels; i++)
{
        CA_ERR(AudioUnitSetParameter(mMixerUnit, kMatrixMixerParam_Volume, kAudioUnitScope_Input, i, 1.0, 0));
}

//Set output channel volumes
for(int i = 0; i < (int)AudioSystem::GetOutputChannelConfig(); i++)
{
        CA_ERR(AudioUnitSetParameter(mMixerUnit, kMatrixMixerParam_Volume, kAudioUnitScope_Output, i, 1.0, 0));
}

该图表开始使用“AUGraphStart()”和“AU GraphStop(无特别意义)”进行并停止。 这里是使用沙克概况收集的电话:

| | | | | | | | | + 1.3%, AudioUnitGraph::Stop(), AudioToolbox
| | | | | | | | | | + 1.3%, AudioOutputUnitStop, AudioUnit
| | | | | | | | | | | + 1.3%, CallComponentDispatch, CarbonCore
| | | | | | | | | | | | + 1.3%, DefaultOutputAUEntry, CoreAudio
| | | | | | | | | | | | | + 1.3%, AUHALEntry, CoreAudio
| | | | | | | | | | | | | | + 1.3%, usleep$UNIX2003, libSystem.B.dylib
| | | | | | | | | | | | | | | + 1.3%, nanosleep$UNIX2003, libSystem.B.dylib
| | | | | | | | | | | | | | | |   1.3%, __semwait_signal, libSystem.B.dylib

它只是睡觉。

任何杂质?