If your compound device supports recording, you might want to let an application open your device without specifying a name for the device element. In this case the application will use the MCI_OPEN_ELEMENT flag and use a zero-length null-terminated string for the element name. Recorded data is not saved in a permanent file until the application explicitly saves it with the MCI_SAVE command. The MCI_SAVE command will specify the name of the destination file.
If your device driver does not support recording without a device element being defined, it should detect the zero length element name and return MCIERR_FILENAME_REQUIRED.