Live captions for OBS and Twitch, generated on your own Mac

Live captions make a stream more watchable — for viewers with the sound off, for anyone who isn’t a native speaker, and for accessibility generally. The usual way to get them is a captioning service: a monthly fee, your microphone audio streamed to somebody else’s servers, and a caption track that stops working when your connection hiccups.

OpenWhisp does it locally instead. The Stream Overlay turns your speech into subtitles on your own machine and serves them to OBS as a normal Browser source.

How it works

When you enable the overlay, OpenWhisp starts a small web server on your Mac (loopback only, port 9280 by default) that serves a single self-contained caption page. Your speech is transcribed on-device and pushed to that page as you talk. OBS just renders a web page — it never needs internet access, and the page pulls in no external assets.

• Open Settings › More features › Stream Overlay and switch on the server.
• Style the captions: font and size, text colour, background (including fully transparent), how many subtitle lines stay on screen, characters per line, and how long captions linger after you stop talking.
• Set the canvas to match your Browser source — 1920×1080 by default.
• Hit Copy URL, add a Browser source in OBS, and paste it with the same width and height.
• Click Start Captions and talk.

The captions behave the way subtitles should: your current sentence word-wraps to the line budget, older lines scroll off the top, and the whole thing fades out after a configurable stretch of silence so you’re not left with a stale sentence frozen on screen.

Captions don’t hijack your keyboard

This is the part that makes it usable while you actually stream. Starting captions runs a hands-free session whose transcript goes only to the overlay — nothing is typed into whatever app happens to be focused. Long silences don’t end it either, so a pause while you read chat won’t kill your subtitles. Stop Captions, Esc, or your normal dictation hotkey ends the session.

Speak one language, caption in another

Because captions run through a normal dictation session, they inherit your language settings — which means the overlay can translate. Switch on Translate to English, download the language pair, and your viewers read English while you speak Russian, Spanish, or any other supported language.

It works with more than OBS

There’s nothing OBS-specific about it. Anything that can display a web page can show the captions — Streamlabs, vMix, a second monitor for an in-person talk, a browser window beside your slides. If your software has a browser or webview source, paste the URL into it.

Why local matters here

Captioning services charge monthly and require your microphone audio to leave your machine — an awkward trade for a private call, a client workshop, or anything under NDA. OpenWhisp’s overlay is a local server on loopback: the audio, the transcription, and the caption page all stay on your Mac, in line with the rest of its on-device approach. It’s also free and open source, so there’s no per-hour meter on your own voice.

Already using OpenWhisp for file transcription and subtitles? This is the live counterpart — same on-device engines, pointed at your stream instead of a file.