docs: def _available_formats_helper(count_flag, format_flag):
      """Helper for available_formats() and available_subtypes()."""
      count = _ffi.new("int*")
      _snd.sf_command(_ffi.NULL, count_flag, count, _ffi.sizeof("int"))
      for format_int in range(count[0]):
          yield _format_info(format_int, format_flag)