How to get Mac audio level?

Question

Currently, I have code that successfully returns the value of the users system audio value that they can set with the volume keys.

However, what I want is a value of the audio the speakers are playing. So if the user is watching Netflix and a character starts screaming, the value would return higher than if the character was whispering.

Code I have now:

+ (AudioDeviceID)defaultOutputDeviceID {
    OSStatus status = noErr;

    AudioDeviceID outputDeviceID = kAudioObjectUnknown;

    AudioObjectPropertyAddress propertyAOPA;
    propertyAOPA.mElement = kAudioObjectPropertyElementMaster;
    propertyAOPA.mScope = kAudioObjectPropertyScopeGlobal;
    propertyAOPA.mSelector = kAudioHardwarePropertyDefaultSystemOutputDevice;

    UInt32 propertySize = sizeof(outputDeviceID);

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

    status = AudioHardwareServiceGetPropertyData(kAudioObjectSystemObject, &propertyAOPA, 0, NULL, &propertySize, &outputDeviceID);

    if(status) {
        NSLog(@"Cannot find default output device!");
    }

    return outputDeviceID;
}

+ (float)volume {
    OSStatus status = noErr;

    AudioDeviceID outputDeviceID = [[self class] defaultOutputDeviceID];

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

    AudioObjectPropertyAddress propertyAOPA;
    propertyAOPA.mElement = kAudioObjectPropertyElementMaster;
    propertyAOPA.mScope = kAudioDevicePropertyScopeOutput;
    propertyAOPA.mSelector = kAudioHardwareServiceDeviceProperty_VirtualMasterVolume;

    Float32 outputVolume;
    UInt32 propertySize = sizeof(outputVolume);

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

    status = AudioHardwareServiceGetPropertyData(outputDeviceID, &propertyAOPA, 0, NULL, &propertySize, &outputVolume);

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

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

    return outputVolume;
}

Answer 1

Get the volume level and set it as you want (as max. volume) and then revert it back again to users original volume level. For more details you can see the below link; https://stackoverflow.com/a/27743599/1351327
Hope it will help. (Be careful that Apple will reject your app)