How Directors Are Chosen For An Ad Film

A script goes out to three or four directors, each comes back with a treatment, and one is chosen. That choice determines more of what the finished film feels like than anything written in the script.
The agency has written the words and the structure. The director decides the performances, the pace, the look, the casting shortlist and the tone, which is most of what an audience actually experiences.
What a treatment is really showing
Not a plan. A treatment is a director explaining what they think the film is about, illustrated with references, and the useful information is in the gap between their reading and yours.
A director who has understood the idea differently from the team is not necessarily wrong. Sometimes their reading is better, and the treatment stage is the cheapest possible place to discover that.
Why the reel misleads
A reel shows a director's best work with the best clients, the best budgets and the best scripts. It does not show what they do with an average brief and half the money.
The more informative question is what they did on a job that went wrong, which nobody puts on a reel and most directors will answer honestly if asked directly.
Every reel is a highlight of the money that was available. Very few of them tell you what the person does when it is not.
Directors specialise, and it is real
Comedy timing, performance with children, food, product macro, scale and spectacle: these are distinct skills, and directors are genuinely better at some than others.
Hiring a visually spectacular director for a film that lives or dies on a two-hander in a kitchen is a common and expensive category error, and it is usually made because the reel was beautiful.
What the pitch conversation should cover
How they intend to cast, how many setups they think the day holds, and what they would cut if time ran short. That last answer reveals their priorities more reliably than any amount of discussion about the idea.
A director who has already decided what is expendable has understood the film. One who says nothing is expendable has not thought about the shoot day.
After the choice
The relationship works when the agency is clear about what is immovable and genuinely open about everything else. Teams that protect every detail get a compliant execution of their storyboard.
Which is a defensible outcome and a waste of the hire. The reason to bring in a director is to get something the room could not have imagined, and that requires leaving room for it.