When the MM_MCIEVENT message is received, the usEventCode field of MsgParam1 contains MCI_MIXEVENT. The pEventData field of MsgParam2 contains a pointer to MCI_MIXEVENT_PARMS. MCI_MIXEVENT_PARMS allows applications to determine the device type that caused the change, the attribute that caused the change (volume, bass, treble, and so on), and the new value of the attribute. A mixer event will also be sent when a connector has been enabled or disabled. The ulConnectorType and ulConnectorIndex fields will indicate the connector that changed and ulConnStatus contains either MCI_TRUE if the connector is enabled or MCI_FALSE if the connector is disabled. If a connector has been modified, ulFlags will contain MCI_MIX_CONNECTOR. If an attribute has been changed, ulFlags will contain MCI_MIX_ATTRIBUTE.
Note: An application must not set an audio attribute while processing the MM_MCIEVENT message. Otherwise a terminal loop will result.