objective c audio meter - objective-c

Question

Is it possible for xcode to have an audio level indicator?
I want to do something like this:
if (audioLevel = 100) {
}
or something similar...
Any ideas?? Example code please?
I'm VERY new to objective c so the more explaining the beter! :D

Answer 1

Unfortunately, there isn't a very straightforward API to do this. You need to use the low level AudioToolbox.framework.
Luckily, others have already solved this problem for you. Here's some code I simplified slightly to be straight C functions, from CocoaDev. You need to link to the AudioToolbox to compile this code (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;
}
Note that there's also a setVolume function there, too.