Guide
How to add subtitles to a video with AI
By Rakshit · Updated
You can add subtitles to a video with AI in three ways: use a platform's own automatic captions, use a tool that produces a subtitle file, or use a clip tool that burns captions into short vertical videos. KeyMo is the third kind. It captions clips word by word in 12 styles, and it is not a caption-only editor.
The three kinds of AI subtitle tool
Search results for an AI subtitle generator mix tools that do quite different things. Sorting them by output saves a lot of trial and error.
| Route | What you get | Pick it when |
|---|---|---|
| Platform auto captions | A caption track the viewer can switch on or off, made by the site that hosts the video | The video stays long and lives on one platform, such as YouTube |
| Caption-file tool | A subtitle file such as SRT or VTT to upload next to the video | You need full-length captions, or captions in a file you can edit and reuse |
| Clip tool with burned-in captions | Short vertical videos with the words drawn into the picture | You are posting to Shorts, Reels or TikTok and want styled, always-on captions |
Most disappointment comes from picking the wrong row. A tool built for one of these jobs may not do another, so decide the output first.
What the AI gets right and wrong
Speech recognition can give you a first draft, but neither YouTube nor the W3C treats it as ready to publish unchecked. YouTube says its automatic captions are made with machine learning, quality varies, and they should always be reviewed and edited. The W3C accessibility guidance says automatic captions do not meet accessibility needs unless they are confirmed fully accurate, and it gives a simple example: one missing "not" can make a caption contradict the audio.
So whichever route you choose, plan to read the result. A short clip has far less text to read than a two-hour video, which is one reason to caption the clips and not the whole recording. We cover that trade-off in adding subtitles to a long video.
Where KeyMo fits, and where it does not
KeyMo starts from a long video, not from a caption file. You upload an MP4 or MOV, or paste a YouTube link on a paid plan, and it finds up to 15 moments, scores each one out of 10, keeps those scoring 7 or higher and renders them as vertical 9:16 clips at 1080x1920. The captions are part of that render: word by word, in one of 12 styles (Pro Glow, Bold Pop, Clean, Punch, Classic, Spotlight, Pulse, Karaoke, Reader, Duo, Slide, Headline), or off.
- Good fit: podcasts, interviews and talks you want to turn into captioned Shorts, Reels and TikToks.
- Not a fit: a caption-only editor, a way to subtitle a video you do not want cut up, or a source of SRT files. We do not claim a separate subtitle-file export, so treat KeyMo as burn-in only.
- Languages: this page makes no claim about which languages KeyMo captions. Check with a short test clip before you rely on it.
- Watermark: none on any plan.
If that matches what you need, the full walk-through is in the clipping guide. To see how the styles look, read the caption styles gallery.
What "free" means here
Many searches add the word free: free subtitle generator, free AI subtitles online. KeyMo has no free plan and no trial. Starter is $12 a month for 300 source minutes and Pro is $29 a month for 900 source minutes, with yearly billing at ten times the monthly price.
If you need a no-cost route, KeyMo is not it. YouTube's help page describes automatic captions on long videos and on Shorts, in a set of languages that includes English, Hindi and Spanish. It does not say how accurate they are, only that quality varies, and it does not list a price, so read YouTube's current terms for what applies to your channel.
A short checklist before you choose
- Decide the output: a track viewers can toggle, a file you keep, or captions drawn into short clips.
- Check the length your source needs. KeyMo takes 5 minutes to 3 hours.
- Check the shape. KeyMo exports vertical only, so a 16:9 deliverable needs another tool.
- Test one real file with your usual audio before you commit to a batch.
- Read the captions on the result. Names, numbers and jargon are where recognition slips.
Sources: YouTube Help: Use automatic captioning (checked 11 October 2026); W3C WAI: Captions/Subtitles (checked 11 October 2026); W3C: Web Content Accessibility Guidelines (WCAG) 2.2 (checked 11 October 2026).