$movies_array = array(
    'title' => $this->input->post('title'),
    'info' => $this->input->post('info')
);
$actors_array = array(
    'name' => $this->input->post('actorname')
);
$movies_actors_array = array();
$this->db->insert('movies', $movies_array);
$movies_actors_array['movies_id'] = $this->db->insert_id();
$this->db->insert('movies', $actors_array);
$movies_actors_array['actors_id'] = $this->db->insert_id();
$this->db->insert('movies_actors', $movies_actors_array);