It all depends on the agency, and what you want to do as the writer. Some agencies simply don't handle film rights, but have sister agencies that do. Some agencies handle everything. Too, some publishers are finicky about film rights, and want to be in the loop, should a film be made.
I retain control of film rights whenever possible because I think it's teh smartes move. This does not mean I'm going to negotiate these rights, it just means I want to be able to say who will negotiate them, when they will be negotiated, etc.
Some agents want 15% of everything, even if someone else negotiates a contract for you. This is wrong.
You always hear about an agent negotiating a contract for the writer, but too few pay enough attention to the contract an agent offers. Most writers are no more able to negotiate a contract with an agent than they're able to negotiate a contract with a publisher.
No matter who offers you a contract, you need someone strictly on your side to go over it. This is where an IP attorney comes in handy. If I sign a contract of any kind, an IP attorney, one who has much experience in such areas, goes over it first.
It isn't just publishers who will write a contract to their advantage, many agents will, and often do, the same.