def get_file_format(self):
        """Get the file format description. This describes the type of
        data stored on disk.
        """
        # Have cached file format?
        if self._file_fmt is not None:
            return self._file_fmt

        # Make the call to retrieve it.
        desc = AudioStreamBasicDescription()
        size = ctypes.c_int(ctypes.sizeof(desc))
        check(_coreaudio.ExtAudioFileGetProperty(
            self._obj, PROP_FILE_DATA_FORMAT, ctypes.byref(size),
            ctypes.byref(desc)
        ))

        # Cache result.
        self._file_fmt = desc
        return desc
Get the file format description. This describes the type of
        data stored on disk.