在屏幕上显示音量控制信息 调用Core Audio APIs 适应于vista win7-This sample uses the Core Audio APIs to implement an on-screen display that shows volume changes to the output stream that plays through the default audio-rendering endpoint device. The on-screen display appears when the user adjusts the volume level in the Windows volume-control program, Sndvol.exe, and it disappears after the volume level remains unchanged for a short period.