# AI agent for making captioned reels

> How an AI agent should write the words on a reel: one burned-in idea versus a transcript dump, and what it must not invent.

Canonical: https://www.runmeg.com/guides/ai-agent-for-making-captioned-reels
Last updated: 2026-10-29

An AI agent for captioned reels should burn one idea into the frame, in the product's words, timed to the moment that proves it. That is different from auto-subtitles, which try to record every word. The agent must not invent a result, a customer, or a promise that was not in the footage or on the site. You still read the line before you post.

The caption is the reel for anyone with the sound off. An agent that only chops video and then pastes the transcript has not done the job the search is asking for.

## Why the caption is the job

On a phone, the default is mute. The line on the picture is the post. The paragraph under the video is optional, and a lot of people never open it. If your agent spends its effort on the description and leaves the frame with tiny subtitles, it optimized the part fewer people read.

A good burned-in line also makes the clip portable. You can send the file to a customer, drop it in a deck, or repost it somewhere that strips the caption field. The meaning travels inside the picture. A transcript that only exists as a platform caption does not.

## Burned-in line versus a transcript dump

Auto-subtitles follow the audio word for word. They are the right tool for a long video where someone needs access to everything that was said. They are the wrong tool for a reel, because they give equal weight to 'um,' the aside, and the offer. The offer ends up in the same size as the throat-clearing.

A marketing line does the opposite. It waits for the moment, or it leads the moment, and it says the point in fewer words than the speaker used. The speaker might take twenty seconds to reach the number. The line can put the number up immediately, as long as the speaker actually said it. You are editing for a stranger, not replacing the talk with a different talk.

Pick the layer on purpose. Many teams need both, and they are written differently.

|  | Burned-in marketing line | Auto-subtitles |
| --- | --- | --- |
| Goal | One reason to stop scrolling | Access to what was said |
| Length | A short line or two | The whole utterance |
| Timing | Held long enough to read | Chases the voice |
| Source | The claim, in your words | The audio, word for word |
| Failure | A slogan nobody said | A readable transcript of nothing |

## What the agent must not invent

It must not invent a metric. If the video says 'a handful of teams,' the caption does not get to say '10,000 teams.' It must not invent a customer logo, a quote, or a comparison you have not published. It must not upgrade a hedge. 'We are testing this with design partners' is not 'everyone is switching.'

It also must not invent a presenter. The person on screen should be someone who was on screen. Generating a face to 'host' your product is a different product category, and it puts words in a mouth you do not have. If the footage is a screen recording with no face, the line can carry it. You do not need a synthetic founder.

```
Allowed
Video: "Three of the teams we onboarded last month were live the same day."
Line: "Three teams last month were live the same day."

Not allowed
Video: "We're hoping more teams get there this quarter."
Line: "Every team is live the same day."

The second line is how an agent 'helps' by deleting the uncertainty. The uncertainty was the truth.
```

## How to brief the caption, not the whole company

The agent should already know the company. Your brief for this run is the angle. 'Use the moment where I show the import. The line should mention same-day, and it should not mention pricing.' That is enough. A brief that restates the homepage is a sign the memory is empty, or that you do not trust it. Fix the memory. Do not write a novel in the prompt.

If you have a never-say list, this is where it earns its place. Captions are short, so one banned word is a large share of the line. Tell the agent the banned word applies to burned-in text, not only to the LinkedIn draft. Otherwise it will behave on the post and show off on the video.

## Read the line at arm's length

Hold the phone at the distance you actually watch from. If you cannot read the line without bringing it closer, the type is a desktop type. Increase the weight or cut the words. Then cover the picture with your hand and read only the text. If it still makes sense, the caption is doing its job. If it needs the pixels to mean anything, the line is a label, not a sentence, and labels do not stop a thumb.

## Where Runmeg fits

ReelGen writes that burned-in line from the product voice, over moments it pulls from a video you upload. It is not an auto-subtitle pass of every word, and it is not a face generator. You download the file and you are the one who posts it. If you already cut the clip and you only want styled subtitles, a dedicated caption tool is the closer match. If you want the line to share a voice with the posts you publish the same week, that is the Runmeg job.

## Questions

### Should marketing captions match the audio exactly?

They should not contradict it. They do not have to transcribe it. Shorten, as long as the stronger sentence is still true.

### Where do accessibility subtitles go?

Keep them as real subtitles or a platform caption when the video is long enough to need them. Do not pretend a six-word hook is a transcript of a webinar.

### Can the agent write the caption in another language?

Only if someone who speaks that language will review it. A caption is a claim. A claim you cannot read is a claim you cannot stand behind.

### What if the best moment has no clean sentence?

Write the line from the fact the moment shows, in your words, and make sure the picture supports it. Do not force a slogan onto a blurry second.

## Related
- [How to add captions to reels](https://www.runmeg.com/guides/how-to-add-captions-to-reels)
- [AI agent for making reels](https://www.runmeg.com/guides/ai-agent-for-making-reels)
- [Runmeg vs Submagic](https://www.runmeg.com/compare/runmeg-vs-submagic)