Bilingual caption studio for Mac
You film in one language.
Your audience reads two.
subline turns speech into styled bilingual captions — transcribed, translated, and burned in on your Mac. No uploads, no credits, no monthly caption allowance.
macOS 15 or later · runs entirely on-device
From footage to bilingual captions in three steps
Drop in a video
subline transcribes the speech on-device and lays the captions out with timings, ready to edit — Cantonese, Mandarin, English, and more.
Translate in place
One click fills every empty translation line using Apple's on-device translation. Lines you have already written are never overwritten.
Style and export
Pick a preset, tune each language separately, and burn the captions into an MP4 — or save an .ass subtitle file instead.
Built for two languages at once
Two languages, two styles
Each language keeps its own font, size, weight, and colour. No single template squeezing both lines into one look.
On-device transcription
macOS speech recognition drafts your captions the moment a video loads. No audio leaves your Mac.
On-device translation
Apple's translation models run locally — download a language pair once, then translate offline. Unmetered, uncounted.
A preview you can trust
The editor and the renderer share one styling definition, so the burned-in result matches the preview exactly.
Waveform timeline
See the speech, not just the clock. Drag captions to move them, pull the edges to retime, click anywhere to seek.
Exports that fit your flow
Burn captions into a finished MP4, or save the raw .ass subtitle file and take it into the rest of your toolchain.
Common questions
Which languages does it support?
Transcription covers the languages macOS speech recognition speaks — including Cantonese, Mandarin, and English. Translation covers every pair Apple's on-device models support; the first use of a pair downloads its model, and after that it works offline.
Does my footage get uploaded anywhere?
No. Transcription, translation, styling, and rendering all run on your Mac. The only network use is Apple's one-time language model downloads.
What do I need to run it?
A Mac running macOS 15 or later. Apple silicon is fastest, and there is nothing else to set up — no account, no API key.
Can I use the captions outside subline?
Yes. Burn them into an MP4 you can cut anywhere, or export a standard .ass subtitle file with all styling and timing intact for tools that read it.