Hook rate
Definition
The share of viewers still watching a video ad after its first seconds, as the platform counts and reports it. It is the earliest number a new creative produces.
How it’s measured
The platform divides the people whose view crossed a threshold of seconds by everyone the ad was shown to. Threshold and label are the platform’s own, published in its documentation and renamed from time to time, so check the current definition before comparing periods. The value of the number is diagnostic. Two failures produce the same poor cost per result: a film nobody stops for, and an offer nobody wants. Hook rate splits them. Low, and the problem is the opening seconds of the film. High with no conversions, and the problem sits downstream, on the landing page or in the offer itself.
What to watch for
A hook rate on its own means nothing; the readable version is your own ads ranked against each other, and the spread tells you whether the openings differ at all. If every video in the account scores within a narrow band, the first seconds are coming off one template and the metric has nothing to compare. When a video holds viewers and still produces no customers, open the landing page it points to on a phone and read whether the page keeps the promise the opening made.
The question you ask
“On the ads that failed, did people stop watching in the first seconds, or did they watch and never buy?”