Nowhere to put an SRT
TikTok, Instagram Reels and YouTube Shorts each accept one video from your camera roll. None of them has a field for a subtitle file, so the sidecar never reaches the viewer.
Auto subtitle app
An auto subtitle app for iPhone
An auto subtitle app transcribes what is said in a video, times each word to the footage, and puts the words on screen for you. Capster does that on the iPhone in about two minutes, in 99 languages it detects by itself, and burns the subtitles into the exported file so it posts anywhere as it is.
25.7 MB · iPhone, iOS 16.0+ · No account · Updated September 2026
What to look for in an auto subtitle app
Six things separate an app you keep from one you delete after a clip. Here they are, and what Capster does about each.
| What it needs | Why it matters | Capster |
|---|---|---|
| Word-level timing, not one block per sentence | Karaoke highlight and one-word captions are impossible without a timestamp per word. | Every word comes back with its own start and end time. |
| Languages beyond English, detected for you | A language picker set wrong costs a whole transcription before you notice. | 99 languages, detected automatically. No picker. |
| An editor for the words it mishears | No speech-to-text gets names and slang right. An app with no editor makes them your problem. | Tap any caption to rewrite it, split the line, or retime it. |
| Captions rendered into the video | A sidecar subtitle file is useless to TikTok, Reels and Shorts, which accept one video and no attachments. | Burned into the frames. One finished file to your camera roll. |
| A preview you can trust | Most editors preview with one renderer and export with another, so the file surprises you after a long render. | The preview runs the same compositor as the export. |
| No account | An account for a video utility is a data liability and a sign-up wall between you and the thing you came for. | There is no sign-in. Nothing identifying you leaves the phone. |
The app doing it
Animation controls, the caption editor, and the style panel.
Animate captions in and out, or pop them word by word.
Tap any caption to fix a word, split a line, or retime it.
Font, size, colour, outline, letter case, word highlight.
How the subtitles get made
Four steps. The only one that leaves the phone is the transcription, and only the audio goes.
- 1
Import
A clip from Photos or Files, copied into the app's own storage. Vertical, square or landscape all work.
- 2
Transcribe
The audio track — not the video — is sent for speech-to-text and comes back word by word with timings, then is deleted at the other end. The privacy policy has the detail.
- 3
Style and correct
9 presets, 18 caption fonts, and an editor for any word the transcription misheard.
- 4
Export
Subtitles rendered into the frames, saved to your camera roll at full quality. Export is never blocked, paid or not.
Auto subtitles versus a subtitle file
Most desktop subtitle tools produce an SRT or VTT file next to your video. That is the right answer for a broadcaster and the wrong one for a phone.
Subtitles you can style are subtitles people read
An SRT carries text and timings and almost nothing else. A burned-in caption can be sized, outlined, boxed and animated so it holds up over the actual footage.
One file, no pairing to lose
Move the exported video anywhere and the subtitles come with it. There is no second file to forget. More on burning subtitles into the video.
Questions people ask
What is an auto subtitle app?
An app that listens to a video's audio, writes out what was said, times each word against the footage, and puts the result on screen as captions. The good ones let you correct the text and control how it looks; the rest hand you a rough transcript and stop there.
Is there an auto subtitle app that works on iPhone alone?
Yes. Capster runs entirely on the iPhone — import, transcribe, style, edit and export, with no desktop step and no file transfer. It needs iOS 16.0 or later and a network connection for the transcription itself; everything else happens on the device.
How accurate is automatic subtitling?
Clear speech in a quiet room transcribes close to perfectly. Accuracy drops with background music, crosstalk, heavy accents and unusual proper nouns. Treat the first pass as a draft: read it, fix the names, and publish. That is thirty seconds against twenty minutes of typing.
Do auto subtitles work in languages other than English?
Capster transcribes 99 languages and works out which one is being spoken by itself. Accuracy varies by language and by how clean the audio is, and captions are machine-generated in every language, so read them before publishing.
What does Capster cost?
Free to download, and free to export from. The free tier covers 5 transcriptions, clips up to 2 minutes and 2 caption styles, with a small badge on exports. Pro is $6.99 a month or $29.99 a year.
Prices and limits in full on the pricing page.
Read next
Subtitles on the next clip you shoot
Import it, wait a minute, read the words, export. No desktop, no account, no subtitle file to lose.
Free to try: 5 transcriptions, clips up to 2 minutes, exports carry a small Capster badge. iPhone, iOS 16.0+. No account.