MIXEROPENDESC

typedef struct tMIXEROPENDESC
{
HMIXER hmx;
LPVOID pReserved0;
DWORD dwCallback;
DWORD dwInstance;
} MIXEROPENDESC;  

The MIXEROPENDESC structure contains information needed by user-mode mixer drivers. The structure is created by winmm.dll and passed to the driver with an MXDM_OPEN message.

Members
hmx
Specifies the client’s handle to the device, as assigned by winmm.dll. User-mode drivers specify this handle as the hDriver parameter to DriverCallback, when sending a callback message.
dwCallback
Specifies the address of a callback function. (See the description of the MXDM_OPEN message.)
dwInstance
Contains the dwCallbackInstance argument that the client specified when calling the mixerOpen function. This value is returned to the client as the dwInstance parameter to DriverCallback.