CoreAudio获取输出采样率 [英] CoreAudio get output sample rate

问题描述

我正在创建一个Mac OS X CoreAudio命令行程序，并通过AudioUnits专有渲染一些字母数字终端输入到实时音频信号中，以保持尽可能简单。所有工作都可以达到匹配输出采样率的水平。

首先，我使用Addisson Wesley的学习核心音频的第07章教程代码CH07_AUGraphSineWave。 / p>

我通过书初始化AudioComponent：

  void CreateAndConnectOutputUnit（MyGenerator * generator）
 {
 
 AudioComponentDescription theoutput = {0}; 
 
 theoutput.componentType = kAudioUnitType_Output; 
 theoutput.componentSubType = kAudioUnitSubType_DefaultOutput; 
 theoutput.componentManufacturer = kAudioUnitManufacturer_Apple; 
 
 AudioComponent comp = AudioComponentFindNext（NULL，& theoutput）; 
 if（comp == NULL）{
 printf（无法获得输出单位）; 
出口（-1）; 
} 
 CheckError（AudioComponentInstanceNew（comp，& generator-> outputUnit），
无法为outputUnit打开组件）; 
 AURenderCallbackStruct输入； 
 input.inputProc = MyRenderProc; 
 input.inputProcRefCon =生成器; 
 CheckError（AudioUnitSetProperty（generator-> outputUnit，
 kAudioUnitProperty_SetRenderCallback，
 kAudioUnitScope_Input，
 0，
& input，
 sizeof（input）， 
 AudioUnitSetProperty失败）； 
 
 CheckError（AudioUnitInitialize（generator-> outputUnit），
无法初始化输出单元）； 
 
} 
  

我的主要问题是我不知道该如何退缩渲染AURenderCallbackStruct
的输出硬件采样率，因为它在信号生成过程中起着至关重要的作用。我无法承受将采样率硬编码到渲染回调中的过程，尽管知道这是最简单的方法，因为速率不匹配会导致信号以错误的音高播放。

有没有办法在如此低级的API上获得默认输出的采样率？
是否可以某种方式进行匹配，而又不会过于复杂？
我想念什么吗？

预先感谢。

致谢，

Tom

解决方案

采样率是所有AudioUnit的属性-请参见 kAudioUnitProperty_SampleRate （文档此处）-尽管最终由IO单元（iOS上为RemoteIO或MacOSX上为HAL单元）驱动音频接口的采样率。这在回调结构中不可用。您需要在初始化代码中使用 AudioUnitGetProperty（）来读取此属性。

在您的情况下，以下内容可能会这样做：

  Float64 sampleRate; 
 CheckError（AudioUnitGetProperty（generator-> outputUnit，
 kAudioUnitProperty_SampleRate，
 kAudioUnitScope_Input，
 0，
& sampleRate，
 sizeof（sampleRate））， 
  

如果您要定位的是iOS，则还需要与音频会话。

I'm creating a Mac OS X CoreAudio command-line program with proprietary rendering of some alphanumeric terminal input into a live audio signal, by means of AudioUnits, trying to stay as simple as possible. All works fine up to matching output sample rate.

As a starting point I'm using the Chapter 07 tutorial code of Addisson Wesley's "Learning Core Audio", CH07_AUGraphSineWave.

I initialize the AudioComponent "by the book":

void CreateAndConnectOutputUnit (MyGenerator *generator) 
{

AudioComponentDescription theoutput = {0}; 

theoutput.componentType = kAudioUnitType_Output;
theoutput.componentSubType = kAudioUnitSubType_DefaultOutput;
theoutput.componentManufacturer = kAudioUnitManufacturer_Apple;

AudioComponent comp = AudioComponentFindNext (NULL, &theoutput);
if (comp == NULL) {
    printf ("can't get output unit");
    exit (-1);
}
CheckError (AudioComponentInstanceNew(comp, &generator->outputUnit),
            "Couldn't open component for outputUnit");
AURenderCallbackStruct input;
input.inputProc = MyRenderProc;
input.inputProcRefCon = generator;
CheckError(AudioUnitSetProperty(generator->outputUnit,
                                kAudioUnitProperty_SetRenderCallback, 
                                kAudioUnitScope_Input,
                                0,
                                &input, 
                                sizeof(input)),
           "AudioUnitSetProperty failed");

CheckError (AudioUnitInitialize(generator->outputUnit),
            "Couldn't initialize output unit");

}

My main problem is in my not knowing how to retreive the output hardware sample rate for the rendering AURenderCallbackStruct since it does play a vital part in the signal generating process. I can't afford having the sample rate hard-coded into the rendering callback, although knowing it's the easiest way, since rate mismatch causes the signal being played at wrong pitch.

Is there a way of getting the default output's sample rate on such a low-level API? Is there a way of matching it somehow, without getting overly complicated? Have I missed something?

Thanks in advance.

Regards,

Tom

解决方案

The sample-rate is a property of all AudioUnits - see kAudioUnitProperty_SampleRate (documentation here) - although ultimately it's the IO Unit (RemoteIO on iOS or HAL unit on MacOSX) that drives the sample-rate at the audio interface. This is not available in the call-back structure; you need to read this property with AudioUnitGetProperty() in your initialisation code.

In your case, the following would probably do it:

Float64 sampleRate;
CheckError(AudioUnitGetProperty(generator->outputUnit,
                                kAudioUnitProperty_SampleRate, 
                                kAudioUnitScope_Input,
                                0,
                                &sampleRate, 
                                sizeof(sampleRate)),

If you're targeting iOS, you also need to interact with the Audio Session.

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