How to get the current volume level of a computer?

Question

How do I access the current Mac volume level from the Cocoa API?

For example: when I use Spotify.app in OS X 10.7 and a sound ad appears and I refuse my Mac volume, the application pauses the ad until I return it to the middle level. I find this incredibly unpleasant and violates user privacy, but somehow Spotify has found a way to do this.

Is there a way to do this with Cocoa? I am creating an application where it may be useful to alert the user if the volume level is low.

Answer 1

. - , , . , :

AudioObjectPropertyAddress propertyAddress = { 
    kAudioHardwarePropertyDefaultOutputDevice, 
    kAudioObjectPropertyScopeGlobal, 
    kAudioObjectPropertyElementMaster 
};

AudioDeviceID deviceID;
UInt32 dataSize = sizeof(deviceID);
OSStatus result = AudioObjectGetPropertyData(kAudioObjectSystemObject, &propertyAddress, 0, NULL, &dataSize, &deviceID);

if(kAudioHardwareNoError != result)
    // Handle the error

kAudioHardwareServiceDeviceProperty_VirtualMasterVolume - :

AudioObjectPropertyAddress propertyAddress = { 
    kAudioHardwareServiceDeviceProperty_VirtualMasterVolume, 
    kAudioDevicePropertyScopeOutput,
    kAudioObjectPropertyElementMaster 
};

if(!AudioHardwareServiceHasProperty(deviceID, &propertyAddress))
    // An error occurred

Float32 volume;
UInt32 dataSize = sizeof(volume);
OSStatus result = AudioHardwareServiceGetPropertyData(deviceID, &propertyAddress, 0, NULL, &dataSize, &volume);

if(kAudioHardwareNoError != result)
    // An error occurred

kAudioDevicePropertyVolumeScalar :

UInt32 channel = 1; // Channel 0  is master, if available
AudioObjectPropertyAddress propertyAddress = { 
    kAudioDevicePropertyVolumeScalar, 
    kAudioDevicePropertyScopeOutput,
    channel 
};

if(!AudioObjectHasProperty(deviceID, &propertyAddress))
    // An error occurred

Float32 volume;
UInt32 dataSize = sizeof(volume);
OSStatus result = AudioObjectGetPropertyData(deviceID, &propertyAddress, 0, NULL, &dataSize, &volume);

if(kAudioHardwareNoError != result)
    // An error occurred

Apple:

kAudioHardwareServiceDeviceProperty_VirtualMasterVolume

Float32, . 0.0 () 1.0 ( ). - HAL. , . , , , . , .

, , , .

Answer 2

CocoaDev , , Cocoa -like:

#import <AudioToolbox/AudioServices.h>

+(AudioDeviceID)defaultOutputDeviceID
{
    AudioDeviceID   outputDeviceID = kAudioObjectUnknown;

    // get output device device
    UInt32 propertySize = 0;
    OSStatus status = noErr;
    AudioObjectPropertyAddress propertyAOPA;
    propertyAOPA.mScope = kAudioObjectPropertyScopeGlobal;
    propertyAOPA.mElement = kAudioObjectPropertyElementMaster;
    propertyAOPA.mSelector = kAudioHardwarePropertyDefaultOutputDevice;

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

    propertySize = sizeof(AudioDeviceID);

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

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

// getting system volume

+(float)volume 
{
    Float32         outputVolume;

    UInt32 propertySize = 0;
    OSStatus status = noErr;
    AudioObjectPropertyAddress propertyAOPA;
    propertyAOPA.mElement = kAudioObjectPropertyElementMaster;
    propertyAOPA.mSelector = kAudioHardwareServiceDeviceProperty_VirtualMasterVolume;
    propertyAOPA.mScope = kAudioDevicePropertyScopeOutput;

    AudioDeviceID outputDeviceID = [[self class] defaultOutputDeviceID];

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

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

    propertySize = sizeof(Float32);

    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;
}