When was the dvd release directed by Billy O'Brien?
CREATE TABLE "films_in_series" (
  "num" real,
  "title" text,
  "maneater" text,
  "television_premiere" text,
  "dvd_release" text,
  "writer" text,
  "director" text,
  "producer" text
);
SELECT "dvd_release" FROM "films_in_series" WHERE "director"='Billy O''Brien';