Question

xcode是否可以有音频电平指示器？

我想做这样的事情：

if (audioLevel = 100) {
}

或类似的......

任何想法？请问示例代码？

我对客观c非常陌生，所以更能解释这个问题！：d

Answer 1

不幸的是，没有一个非常简单的API可以做到这一点。您需要使用低级AudioToolbox.framework。

幸运的是，其他人已经为你解决了这个问题。这里有一些代码我从CocoaDev稍微简化为直接C函数。您需要链接到AudioToolbox才能编译此代码（see here for documentation on how to do so）。

#import <AudioToolbox/AudioServices.h>

AudioDeviceID getDefaultOutputDeviceID()
{
    AudioDeviceID outputDeviceID = kAudioObjectUnknown;

    // get output device device
    OSStatus status = noErr;
    AudioObjectPropertyAddress propertyAOPA;
    propertyAOPA.mScope = kAudioObjectPropertyScopeGlobal;
    propertyAOPA.mElement = kAudioObjectPropertyElementMaster;
    propertyAOPA.mSelector = kAudioHardwarePropertyDefaultOutputDevice;

    if (!AudioHardwareServiceHasProperty(kAudioObjectSystemObject, &propertyAOPA))
    {
        printf("Cannot find default output device!");
        return outputDeviceID;
    }

    status = AudioHardwareServiceGetPropertyData(kAudioObjectSystemObject, &propertyAOPA, 0, NULL, (UInt32[]){sizeof(AudioDeviceID)}, &outputDeviceID);

    if (status != 0) 
    {
        printf("Cannot find default output device!");
    }
    return outputDeviceID;
}

float getVolume () 
{
    Float32 outputVolume;

    OSStatus status = noErr;
    AudioObjectPropertyAddress propertyAOPA;
    propertyAOPA.mElement = kAudioObjectPropertyElementMaster;
    propertyAOPA.mSelector = kAudioHardwareServiceDeviceProperty_VirtualMasterVolume;
    propertyAOPA.mScope = kAudioDevicePropertyScopeOutput;

    AudioDeviceID outputDeviceID = getDefaultOutputDeviceID();

    if (outputDeviceID == kAudioObjectUnknown)
    {
        printf("Unknown device");
        return 0.0;
    }

    if (!AudioHardwareServiceHasProperty(outputDeviceID, &propertyAOPA))
    {
        printf("No volume returned for device 0x%0x", outputDeviceID);
        return 0.0;
    }

    status = AudioHardwareServiceGetPropertyData(outputDeviceID, &propertyAOPA, 0, NULL, (UInt32[]){sizeof(Float32)}, &outputVolume);

    if (status)
    {
        printf("No volume returned for device 0x%0x", outputDeviceID);
        return 0.0;
    }

    if (outputVolume < 0.0 || outputVolume > 1.0) return 0.0;

    return outputVolume;
}

int main (int argc, char const *argv[])
{
    printf("%f", getVolume());
    return 0;
}

请注意，那里也有一个setVolume函数。

客观c音频表

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