The short answer
For Veo 3 and Veo 3.1, write dialogue as a single short line spoken by a single visible speaker. Keep the line to roughly 8 seconds of speech or less, name the speaker and delivery, ask for clear lip-sync, and state: no other voices, no music over the line, no on-screen text. If a line is rushed or cut off, shorten the line first — do not rewrite the whole scene.
Copy-ready template
A medium close-up of [one speaker, with appearance]. [He/She] looks toward camera and says: "[one short line]" — delivery is relaxed and conversational, with clear lip-sync. Locked camera. [Setting and light]. Faint ambient sound only; no other voices, no music, no on-screen text.
Why lines get cut off
- Too much speech for the clip. Two lines, or one long sentence, do not fit a short generation.
- Speaker not in frame. If the face is out of shot, the model has nowhere to put the voice.
- Competing audio. Music, crowd voices and a spoken line at once usually degrade all three.
- Changing five things at once. After a bad take, change one variable — usually line length — and reroll.
Fix it with the generator
Use the Veo 3 Prompt Generator, set Audio to Dialogue, and keep the dialogue field to one short line. Price: free ($0), no sign-up — see pricing.