Short-form video is watched muted. Captions aren't an accessibility extra there — they're how the video gets understood at all.
Both apps have their own auto-caption feature, and both have the same three limits: the captions only exist inside that app, the styling is whatever they offer, and you have to upload the video before you can see them. If you want the same captions on Reels, TikTok, Shorts and your own site, the text has to be in the picture before you upload.
Why you can't just upload an .srt
Instagram and TikTok don't accept subtitle files. YouTube does accept one for a regular video upload — but on a feed that autoplays muted, a caption track the viewer has to switch on doesn't help you.
So for short-form: burn the captions in. See separate file vs burned in for when each one applies.
Step by step, free and without uploading
OpenSubs runs in a browser tab, so the clip stays on your machine.
1. Export your vertical clip first
Cut and frame the video however you normally do — phone, CapCut, Premiere — and export it at 9:16. OpenSubs draws captions onto the video you give it; it doesn't reframe or crop, so do that first.
2. Open it in OpenSubs
Go to opensubs.app and choose the file. Nothing is uploaded.
3. Generate the captions
Click Generate from the audio. Speech recognition runs on your own machine; the language is detected automatically. A 30-second clip is quick.
4. Read them through
Short-form is dense and fast, and names and slang are where automatic transcripts slip. Fix any line by typing in it.
5. Pick a style built for a phone screen
Choose a caption style — the big, heavy presets are the ones that hold up on a small screen. A couple of things worth doing:
- Turn on word-by-word highlighting if you want the bouncing-word look that short-form audiences are used to. See word-by-word captions.
- Keep captions clear of the interface. Both apps put buttons down the right side and text along the bottom; anything in those zones gets covered.
- Preview it over your own footage before you export — what you see is what gets drawn.
6. Burn and post
Click Burn subtitles into the video, save the MP4, and upload that. No watermark, no account.
If you also want the subtitle file — for a YouTube upload of the same cut, or for translation — export the .srt at the same time. The timings match.
Posting the same clip in another language
Translate the subtitles before burning: pick a target language, and in Chrome the translation runs on your device at no cost. You can either replace the original text or keep both lines on screen, which is common for creators posting to two audiences at once.
Caption habits that work in short-form
- Short cues. A few words at a time, matching the pace of the speech.
- High contrast. White text with an outline, or a solid box behind it, survives busy footage.
- Keep the top and bottom strips clear — that is where both apps put their own text and buttons.
- Don't caption every "um". Clean it up while you're reading through.
FAQ
Does OpenSubs crop my video to 9:16?
No. Export the vertical version first; OpenSubs adds the captions.
Will there be a watermark?
No.
Can I use it on a phone?
The app runs in a browser and the encoding is heavy; a laptop or desktop is the realistic way to do it.
Are my videos uploaded anywhere?
No. Transcription and burning both run in your browser tab.
Can I edit the captions after burning them in?
Not in the exported MP4 — they're part of the picture. Keep the subtitle file and re-export.