Efficient Compute
How to add subtitles to a video on iPhone automatically
iOS has no built-in way to write captions into a video, so you need an editor that transcribes speech: import the clip, run transcription, correct the proper nouns and numbers, style the captions for a muted viewer, then export. Talk does this on-device in 31 languages and includes it on the free tier.
The steps
- Import and transcribe In Talk, either open Smart Edit → Transcribe or just ask for captions in plain language. Transcription runs on the device, so the audio never leaves the phone.
- Set the spoken language before transcribing Not after. Automatic detection is fine for common languages but costs you a full pass when it guesses wrong, and accented speech is exactly the case it misreads.
- Fix proper nouns and numbers first Names, brands, technical terms, and figures are where automatic transcription is reliably wrong, and they are also the errors viewers notice. Ordinary sentences rarely need touching. Reading the whole transcript word by word is a poor use of your time; scanning for capital letters and digits is a good one.
- Style for someone watching with the sound off Most social video is consumed muted, which makes captions the primary channel rather than an accessibility afterthought. Large, high-contrast, and inside the safe area so the platform’s own interface does not cover them.
- Export Exporting burns the captions into the picture, which is what social platforms need. Talk exports 1080p free with no watermark; 4K and HDR need Pro.
Burned-in captions or a subtitle file?
These are different products and the choice is determined by where the video is going, not by preference.
| Burned-in captions | Drawn into the video pixels; cannot be switched off. Required in practice for TikTok, Instagram Reels, and YouTube Shorts, where most viewing is muted and autoplay gives you no chance to enable anything. Invisible to search engines, because it is picture, not text. |
|---|---|
| Subtitle file (SRT / VTT) | Separate text the player overlays and the viewer can disable. The right choice for YouTube long-form, for genuine accessibility, and for discoverability — a subtitle file is machine-readable, so it feeds search and gives you a transcript for free. |
For a video going to more than one platform, transcribe once and use the transcript both ways: burn captions in for the vertical cut, and upload the file alongside the long-form version.
Where automatic transcription fails
Accuracy claims of “99 percent” are marketing. For clear speech in a common language, expect 85 to 95 percent of words correct. It degrades predictably:
- Accents that differ from the model’s training distribution
- Background noise — running on-device voice isolation first usually helps more than switching apps
- Overlapping speakers, which most mobile transcribers do not separate at all
- Technical vocabulary and brand names, which get replaced with common words that sound similar
- Numbers, especially prices, dates, and version numbers
None of this makes automatic captioning a bad idea. It makes an unreviewed caption track a bad idea.
Which iPhone apps transcribe automatically
| App | Auto-captions | On-device? | Free tier |
|---|---|---|---|
| Talk | Yes, 31 languages | Yes | Yes, no watermark, 1080p |
| CapCut | Yes | No | Yes |
| Captions.ai | Yes, strong styling | No | Limited |
| Adobe Premiere for iPhone | Yes | No | Limited |
| Wavcut | Yes | Yes on free, cloud on paid | Yes, with caps |
| iMovie | No | — | Free, but manual text only |
On-device matters if your footage is confidential, covered by an NDA, or contains someone else’s personal information. If it does not matter to you, cloud transcription is often slightly more accurate. Check the current App Store listing before subscribing — these change frequently.
Frequently asked questions
Can an iPhone add subtitles to a video automatically?
Yes, with a third-party editor. iOS has no system feature that writes captions into a video. Talk, CapCut, Captions.ai, Adobe Premiere for iPhone, BlitzCut, and Wavcut all transcribe automatically; iMovie does not.
How accurate is automatic subtitling?
Roughly 85 to 95 percent of words for clear speech in a common language. Accents, noise, fast or overlapping speech, and technical vocabulary all reduce it. Proper nouns and numbers are least reliable.
Does automatic captioning upload my audio?
Depends on the app. Talk transcribes on-device in 31 languages. Others send audio to a server. Check the privacy disclosure rather than assuming.
What is the difference between captions and a subtitle file?
Burned-in captions are part of the picture and cannot be turned off — what short-form platforms need. An SRT or VTT file is separate text the viewer can disable, and it is machine-readable, which is better for YouTube and accessibility.
Can I get subtitles in a different language from the audio?
Yes — transcribe, then translate. Talk can translate a transcript and can dub the audio into another language, though dubbing sends data off-device because the model is too large to run locally.
Are automatic subtitles free on iPhone?
Some are. Talk includes them free with no watermark at 1080p, as does CapCut. Captions.ai and Adobe require a subscription.