Alarm/event information callback function.
typedef void(CALLBACK *MSGCallBack)( LONG lCommand, NET_DVR_ALARMER *pAlarmer, char *pAlarmInfo, DWORD dwBufLen, void *pUser );
[OUT] Uploaded message type. You can distinguish the alarm/event information via the type.
[OUT] Alarm device information, including serial No., IP address, login handle, and so on, see details in NET_DVR_ALARMER.
[OUT] Alarm/event information, the details are returned in different structures according to lCommand.
[OUT] Size of alarm/event information buffer.
[OUT] User data.