ulParam1 (ULONG)

      This parameter can contain any of the following flags:

      MCI_NOTIFY

        A notification message will be posted to the window specified in the hwndCallback parameter of the data structure pointed to by the pParam2 parameter. The notification will be posted when the action indicated by this message is completed or when an error occurs.
      MCI_WAIT
        Control is not to be returned until the action indicated by this message is completed or an error occurs.
      Video Overlay Extensions

      MCI_OVLY_FREEZE_RECT

        The rect field of the data structure identified by pParam2 contains a valid rectangle. If the MCI_OVLY_FREEZE_RECT parameter is not specified, the entire video destination rectangle is unfrozen.
      MCI_OVLY_FREEZE_RECT_OUTSIDE
        Indicates the area outside the specified rectangle is to be unfrozen.

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