typedef struct ACP_MESSAGE {  
    UINT32 type;  
    UINT32 droppedMessageCount;  
    UINT32 usec;  
    union  
    {  
        ACP_MESSAGE_AUDIO_FRAME_START audioFrameStart;  
        ACP_MESSAGE_FLOWGRAPH_COMPLETED flowgraphCompleted;  
        ACP_MESSAGE_SHAPE_COMMAND_BLOCKED shapeCommandBlocked;  
        ACP_MESSAGE_COMMAND_COMPLETED commandCompleted;  
        ACP_MESSAGE_FLOWGRAPH_TERMINATED flowgraphTerminated;  
        ACP_MESSAGE_ERROR error;  
    };  
} ACP_MESSAGE