无法在格式转换器音频单元上设置格式。

Question

我正在尝试建立一个非常简单的AU图--简单地说，是一个带有变体的RemoteIO，用于输出。不幸的是，我似乎无法在变体单元上设置音频格式。我看到的其他例子似乎没有麻烦地设置了格式。我得到的确切错误是不支持的格式。但是，RemoteIO单元内的格式转换器将很高兴地采用my格式，这是一种简单的16 the 16位签名的int格式。

下面是我目前正在努力工作的代码：

 // Describe the output unit.
AudioComponentDescription inputDescription = {0};   
inputDescription.componentType = kAudioUnitType_Output;
inputDescription.componentSubType = kAudioUnitSubType_RemoteIO;
inputDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
AUNode ioNode;
CheckError(self, AUGraphAddNode(_graph, &inputDescription, &ioNode), "Couldn't add ioNode to AU graph");

AudioComponentDescription varispeedDescription = {0};
varispeedDescription.componentType = kAudioUnitType_FormatConverter;
varispeedDescription.componentSubType = kAudioUnitSubType_Varispeed;
varispeedDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
AUNode varispeedNode;
CheckError(self, AUGraphAddNode(_graph, &varispeedDescription, &varispeedNode), "Couldn't add varispeed node to AU graph");

CheckError(self, AUGraphOpen(_graph), "Couldn't open AU graph");
AudioUnit varispeedUnit;
CheckError(self, AUGraphNodeInfo(_graph, varispeedNode, NULL, &varispeedUnit), "Couldn't get varispeed audio unit");

CheckError(self, AUGraphNodeInfo(_graph, ioNode, NULL, &_ioUnit), "Couldn't get io unit");

// Enable input
// TODO: Conditionally disable input if option has not been specified
UInt32 one = 1;
CheckError(self, AudioUnitSetProperty(_ioUnit,
                                 kAudioOutputUnitProperty_EnableIO,
                                 kAudioUnitScope_Input,
                                 kInputBus,
                                 &one,
                                 sizeof(one)), "Couldn't enable IO on the input scope of output unit");

// TODO: check this works on iOS!
_format.mBitsPerChannel = 16;
_format.mBytesPerFrame = 2;
_format.mBytesPerPacket = 2;
_format.mChannelsPerFrame = 1;
_format.mFramesPerPacket = 1;
_format.mReserved = 0;
_format.mSampleRate = 16000.0;
_format.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
_format.mFormatID = kAudioFormatLinearPCM;

self.samplingRate = _format.mSampleRate;
UInt32 size;
size = sizeof(AudioStreamBasicDescription);
CheckError(self, AudioUnitSetProperty(_ioUnit,
                                kAudioUnitProperty_StreamFormat,
                                kAudioUnitScope_Output,
                                kInputBus,
                                &_format,
                                size),
           "Couldn't set the ASBD on the audio unit (after setting its sampling rate)");
size = sizeof(AudioStreamBasicDescription);
CheckError(self, AudioUnitSetProperty(varispeedUnit,
                                      kAudioUnitProperty_StreamFormat,
                                      kAudioUnitScope_Output,
                                      0,
                                      &_format,
                                      size),
           "Couldn't set the ASBD on the audio unit (after setting its sampling rate)");
size = sizeof(AudioStreamBasicDescription);
CheckError(self, AudioUnitSetProperty(varispeedUnit,
                                      kAudioUnitProperty_StreamFormat,
                                      kAudioUnitScope_Input,
                                      0,
                                      &_format,
                                      size),
           "Couldn't set the ASBD on the audio unit (after setting its sampling rate)");

我还尝试简单地设置RemoteIO输出总线的输入格式，它对转换器的输出格式很好，但它仍然不接受我的格式作为转换器的输入格式。

如何将变体和RemoteIO与我想要的格式连接起来？

Answer 1

我发现在一个旧的邮件列表中，Varispeed单元仅是浮点，实际上并不进行格式转换，尽管主要类型是FormatConverter。解决方案是使用另一个带有专用转换器子类型的转换器将我自己的格式转换为Varispeed想要的FP格式。Varispeed的格式限制实际上并不是我所能知道的任何地方，所以我不知道它到底想要什么格式，除了扬声器输出格式对我有用，它应该是浮点线性PCM格式。

而仅供参考，Varispeed单元不做任何音高校正，这听起来很荒谬，当改变播放率。您可以使用NewTimePitch单元代替，它响应相同的变量参数，但结果听起来不像废话。