Two jobs a voice can do
A voice over is any voice heard over the picture by someone who is not on screen. It is usually short and placed where it is needed: a line under a product shot, a tagline at the end of an ad, a few sentences that introduce a segment. The visuals carry the piece and the voice supports them.
Narration is a voice over that carries the piece. The narrator guides the viewer from start to finish, explains what they are seeing, and connects one scene to the next. Documentaries, explainers, courses, and audiobooks are narrated; take the voice away and the video stops making sense.
How they differ in practice
The practical difference is length and continuity. A voice over for an ad may be a few hundred characters. A ten-minute narration is roughly 10,400 characters, read in one consistent voice, with the same pace and pronunciation from the first minute to the last.
- Script: voice over lines are written around the edit; narration is written first and the edit follows it.
- Delivery: voice over can be punchy and stylized; narration needs a steady, listenable pace over many minutes.
- Consistency: a voice over can be re-recorded line by line; narration has to sound like one read even when sections are redone.
- Timing: voice over is placed against cuts; narration usually sets the timing that the cuts follow, often with subtitles.
Which one your video needs
Ask what happens if you mute the voice. If the video still works, you need a voice over: short lines that add emphasis or a call to action. If it falls apart, you need narration, and the script deserves the same care as the visuals.
- Ads, product teasers, intros, and social clips: voice over.
- Documentaries, history and science channels, and video essays: narration.
- Courses, tutorials, and onboarding videos: narration, with consistent terminology across lessons.
- Audiobooks and long-form fiction: narration at its longest.
Choosing an AI voice for each
For a short voice over, almost any good AI voice works, because a few lines rarely expose inconsistency. Pick the voice whose character fits the brand and regenerate a line until it lands.
Narration asks more of the tool. The whole script should stay in one project with one voice and fixed settings, names and terms should be pronounced the same way every time, a changed sentence should be fixable without redoing the full read, and subtitles should come from the final audio. Those are the things to test with a full-length script before committing a series to any AI narrator.