Privacy Policy

Last updated: 2026-10-11

Twinsub (双语幕) is a subtitle tool that runs locally on your Mac. This page explains what it touches and what it does not.

1. Your videos, audio and subtitles

Videos, audio and the subtitles generated from them are processed only on your Mac and are never uploaded to any server. We have no backend, so we cannot see your files, file names or subtitle text. Subtitle files are written to the folder you authorized, which is where your video is.

2. Live subtitles and the microphone (microphone from version 1.1)

Live subtitles work on the sound that is playing on your Mac (all apps, or one app you pick). Starting with version 1.1 you can also choose the microphone as the audio source, for in-person meetings and face-to-face conversations. The microphone is used only when you have chosen it as the source and live subtitles are running. Whatever the source, audio is used only on your Mac for recognition and translation: it is not recorded, not saved and not uploaded.

Subtitle text is not saved by default. Starting with version 1.1 you can choose to save a session's subtitles as a text file, to a location you pick; we never receive it. Capturing computer audio and using the microphone both require your permission in macOS, which you can withdraw at any time in System Settings.

Meetings involve other people's speech. Before you save text, or use live subtitles where people need to be told, please follow the rules of your region and organization.

3. Model download

The speech recognition model is downloaded on first use from dl-twinsub.gatheon.com. That address is hosted on Cloudflare and, like any website, produces routine access logs (IP address, time, requested file). We do not link these logs to your videos, subtitles or identity.

4. Translation

Translation uses Apple's on-device translation, so text does not leave your Mac. Language packs are downloaded from Apple by macOS.

5. Anonymous usage statistics

The app sends anonymous usage events through PostHog, such as whether a transcription succeeded or failed, video length (in ranges), time taken, how live subtitles are used (the type of audio source and roughly how long), and the system version. We use them to find and fix problems. Events contain no file names, file paths, subtitle text or audio, and no name or account. Events tell devices apart with a random number the app generates on your Mac. It is not an advertising identifier, and it is not tied to your account, your Apple ID or any other app. You can turn this off at any time in the app's settings.

In terms of the App Store privacy label, we collect three kinds of data: identifiers (a device ID, the random number above), usage data (product interaction) and diagnostics (performance data). All three are used for analytics only, are not linked to your identity, and are not used for tracking: we do not combine them with data from other companies' apps or websites, use them for advertising, or share them with data brokers.

6. This website

This website uses Google Analytics (served through Gatheon's own domain, with IP anonymization on), PostHog and Cloudflare Web Analytics to measure visits and clicks, without personal identity information. PostHog does not collect when your browser sends Do Not Track.

7. Purchases

The one-time purchase is an Apple in-app purchase. Apple handles payment and billing; we never receive your payment details.

8. Contact

For any privacy question, write to twinsub@gatheon.com.