🎬 Video · Captions · AI Productivity
AI Tool to Add Subtitles to Video, Free and Without a Watermark
(Method + 2 Prompts)
You want an AI tool to add subtitles to your video, free, with no logo stamped on the export. That is a fair goal, but the answer is not one product name. Free plans, limits and watermark rules change often, so any list goes out of date fast. This guide gives you something that lasts: two ways to get captions, a way to avoid the watermark problem completely, a checklist to test any tool, and two prompts that do the text work.
Two kinds of captions: in the picture, or in a file
Before you pick a tool, pick the type. They behave very differently.
| Type | What it is | Good for | Weak spot |
|---|---|---|---|
| A. Burned-in (open) captions | Text drawn on the video. It is part of the picture. | Reels, shorts and ads, where viewers scroll with sound off | You cannot turn them off. A typo means re-exporting the video. |
| B. Caption file (such as SRT) | A small text file with lines and times. The platform shows or hides it. | Tutorials, lessons, longer videos, several languages | Not every platform accepts a file, and you cannot style it as freely. |
Why a caption file sidesteps the watermark problem
A watermark is stamped on the video that a tool exports. If the tool never exports your video, there is nothing to stamp. With a caption file, you keep your original video, get only the text file, and upload both to the platform yourself. The platform then shows the captions on top of your clean video.
This is a general method, not a feature of any one product. It only works where the place you publish lets you add a caption file, so check that first. If you need burned-in text, the export is where a logo can appear, and the next section helps you test for that.
The check-before-you-commit table for any subtitle tool
We do not list products or promise what they offer, because free plans change. Run any tool through these questions with a short test clip before you spend an evening on it.
| Question | Why it matters | How to check |
|---|---|---|
| Does the free export carry a logo? | This is the whole reason you are here | Export a 10-second test and watch the whole frame |
| Maximum video length? | Free plans often cap minutes | Read the plan page and the upload screen |
| Maximum resolution? | A cap can make vertical video look soft | Check the export size on your test file |
| Can I download the caption file? | A file lets you fix text anywhere | Look for an SRT or similar download |
| Which languages? | Accuracy differs by language and accent | Test with your own voice |
| Is my video stored or shared? | Matters for client or private content | Read the privacy page before uploading |
The five-step caption workflow
- Get a transcript. A tool or a speech-to-text feature gives you the spoken words. For options, see AI meeting transcription tools.
- Fix the transcript. Correct names, numbers, product words and jargon before anything else.
- Break it into short lines. Use the first prompt below.
- Time the lines. Most tools set times for you. If you work in text, add times yourself or let the editor align them.
- Review on a phone with the sound off. Can you follow the video? Is any line too fast, too small or in the way?
Fixing first and splitting second saves work. A typo fixed once in the transcript does not have to be fixed in thirty caption lines.
Prompt 1: turn a transcript into caption lines
Use a free chatbot such as ChatGPT, Claude or Gemini. Paste your corrected transcript.
Turn this transcript into caption lines for a short video.
Rules: about 40 characters per line, two lines maximum per caption.
Split at natural phrases, never in the middle of a name or a number.
Do not change, add or remove any spoken words. Keep the original order.
Put a blank line between captions. Do not add times.
Transcript:
[paste corrected transcript]
Prompt 2: fix mistakes in a caption file without moving the timings
Use this when you already have an SRT file with errors in the words.
Below is a caption file. Fix spelling, wrong words and punctuation only.
Do NOT change any number, any timing line (00:00:00,000 --> 00:00:00,000) or the caption order.
Keep each caption to two lines of about 40 characters.
Correct spellings: [list names, brand words, jargon].
After the file, list every change you made.
Caption file:
[paste SRT text]
Read the change list. If the bot touched a timing line or a number, reject that version.
Style rules that keep captions readable
- Contrast. Use light text on a dark box, or dark text on a light box. Test it over the brightest and darkest frames.
- Safe area. Keep text away from the edges. On vertical video, platform buttons and titles cover parts of the screen, so leave room at the bottom and sides.
- Do not cover faces or key visuals. Move captions up or down when a product, a price or a face sits where they land.
- Size. If you must squint on a phone, make it bigger.
- Pace. Give each caption enough time to read once. Very short flashes tire the eye.
A fictional 45-second product video
This is made-up (fictional). A small shop, "Green Cup Co.", has a 45-second ad for a reusable coffee cup. The owner wants captions and has no budget for a plan.
- She exports a transcript and fixes "green cup co" to the real spelling and "$18" where the tool wrote "eighty".
- Prompt 1 gives about 14 captions of two short lines each.
- She downloads an SRT and uploads it to the platform with her clean video, so no export stamp appears.
- On her phone with the sound off, she sees one caption sits over the price tag. She edits the file, and checks again.
The same text could also be burned in for a reel, after a test export shows no logo.
Fix list: common AI caption errors
| If the caption... | Do this |
|---|---|
| Misspells your brand or a name | Fix it once in the transcript, then redo the split |
| Hears a number wrongly ("15" for "50") | Check every price, date and quantity against the audio |
| Turns jargon into a similar common word | Give the bot a word list in Prompt 2 |
| Splits a name or phrase across two captions | Move the line break before the phrase |
| Appears before or after the voice | Shift the time in your editor |
| Has no punctuation and reads as a wall | Add commas and full stops, then shorten lines |
| Skips sounds that matter, like music or a laugh | Add a short note in square brackets if it helps the viewer |
Captions are an access feature, not only a style
Captions help people who are deaf or hard of hearing, people watching in a noisy or quiet place, and viewers who are learning your language. A caption file also lets a viewer turn captions on or off, which burned-in text does not. For anything people rely on, such as a lesson or a safety video, a correct caption file is the safer choice. Rules about required captions differ by country and use, and this is not legal advice.
Once your video has clean text, you can reuse it. See writing a YouTube video script to plan the next one, or turning a blog post into a YouTube video.
When not to use AI for this:
Do not publish AI captions without a full watch for legal, medical, safety or money content, or any video where one wrong word or number can mislead. Also be careful with strong accents, many speakers or noisy audio, where errors rise. Do not upload private or client video to a tool until you have read its privacy terms.