public static extern uint waveOutGetDevCaps(IntPtr hwo,ref WAVEOUTCAPS pwoc,uint cbwoc);

Declare Auto Function waveOutGetDevCaps Lib "winmm.dll" (ByVal uDeviceID as Integer, ByRef lpCaps As WAVEOUTCAPS, _

         ' waveOutGetDevCaps(i, wc, Len(wc))

         waveOutGetDevCaps(i, wc, System.Runtime.InteropServices.Marshal.SizeOf(wc))  

            waveOutGetDevCaps(uDeviceID, ref waveOutCaps, Marshal.SizeOf(typeof(WAVEOUTCAPS)));

    public static extern uint waveOutGetDevCaps(int hwo, ref WAVEOUTCAPS pwoc, /*uint*/ int cbwoc);