The brief is already in your head. Typing it is what stalls. The voice agent writes the campaign from the conversation, so the first artifact you touch is a draft to edit rather than a blank page to fill.
The path
Talk, then problem statement and hypotheses, then ad angles, then a campaign you can spend against. Each step inherits the specificity of the one before it, which is why the recording matters more than it seems to.
Why the spoken version is better
Ask a founder to explain an idea in conversation and you get a named person, a specific frustration, an example from last week. Ask the same founder to write it down and you get a paragraph about unlocking efficiency. The argument is in talking is faster than typing.
See voice agent and ads and campaigns, or the step-by-step in how to turn a voice memo into an ad campaign.