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Hi,
I want to get&set the
input&output volume of a USB audio device, This USB audio device
was recognised by MAC OSX(MAC Mini), and I can adjust it's
Input&output volume in "System preferences". But when I
try to control it's valume in my programme, I meet err. I don't
know why and what should i do.I wrote code like this :
//----------------------------------------------------------------------------------
//
To get the list of devices, you follow these three
steps:
//1. You get the size of the list.
int
theSize;
OSStatus err;
err =
AudioHardwareGetPropertyInfo
(
kAudioHardwarePropertyDevices,
&theSize,
NULL );
int theNumberDevices = 0;
theNumberDevices =
theSize / sizeof(AudioDeviceID);
//2. You allocate enough
space to hold the list.
AudioDeviceID*
theDeviceList;
theDeviceList = (AudioDeviceID*) malloc
(
theNumberDevices * sizeof(AudioDeviceID)
);
//3. You get the device list.
err =
AudioHardwareGetProperty
(
kAudioHardwarePropertyDevices,
&theSize,
theDeviceList );
//4. Get the devices' name
int
i;
for(i = 0; i < theNumberDevices;
i++)
{
int iSizeName = 0;
AudioDeviceGetPropertyInfo(
theDeviceList[i],
0,
false,
kAudioDevicePropertyDeviceName,
&iSizeName,
NULL);
char *cName = (char
*)malloc(iSizeName);
err=
AudioDeviceGetProperty(theDeviceList[i], 0,
false,
kAudioDevicePropertyDeviceName,
&iSizeName,cName);
int
t = 0;
}
// To set the volume of a channel, you
follow these steps:
// 1. You find out if output channel 2
has a volume control.
bool isWritable;
err =
AudioDeviceGetPropertyInfo (
theDeviceList[1], 2,
false, // theDeviceList[1]'s name = "Generic USB Audio
Device"
kAudioDevicePropertyVolumeScalar,
NULL,
&isWritable );
// 2. If it does have a volume control,
you set the value.
if ( (err == kAudioHardwareNoError)&&
isWritable)
{
float theValue = 0.8;
err
= AudioDeviceSetProperty (
theDeviceList[1], NULL, 2,
false,
kAudioDevicePropertyVolumeScalar,
sizeof(float),
&theValue ); // Sometimes the volume can
be changed, but sometimes nothing happend.
// I'm sure this
code has been executed every
time
}
//----------------------------------------------------------------------------------
And the other question: What dose the 2ed param of
AudioDeviceGetProperty (idChannel) indicate?
How can i get&set this param?
Thanks advanced!
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