Free AI subtitles for Stremio when none exist in your language

Updated 2026-10-29

Subtitle Sync for Stremio translates a subtitle into your language with AI when none exists in any of your languages. It is free: it uses your own free Google Gemini key, with no card. If you have a DeepL API key, DeepL can translate instead, or next to Gemini. The translated subtitle is timed to the exact video you are playing whenever the addon can read that timing, it shows at the top of the subtitle menu, and it usually starts translating as soon as the list appears. Each translation is kept, so the next person watching with the same subtitle gets it at once, even without a key.

When is a subtitle translated?

Only when none of your chosen languages has a subtitle on any of your subtitle sites. Subtitles that people wrote in your language always come first: if you chose Serbian and Croatian and only a Croatian one exists, you get that one and nothing is translated. To always get your first language instead, tick “Translate into … even when my other languages have subtitles” under Advanced options on the setup page.

So the translation is for what nobody has subtitled in your language yet: new episodes, older or smaller films, and languages with few subtitles.

Chinese is the one exception: a subtitle in the other script does not count. Someone reading Traditional Chinese (繁體中文) who only finds Simplified (简体中文) gets a translation into Traditional on top, written with Taiwan’s words, and the Simplified one right under it; the same the other way round.

Which subtitle is it translated from?

Subtitle Sync for Stremio picks the subtitle that translates best, in this order:

1. A subtitle made for your very file, in any language.
2. A subtitle in a language nearly the same as yours: Croatian, Bosnian or Montenegrin for Serbian (and the other way round), Danish or Swedish for Norwegian, Ukrainian for Russian, Brazilian for European Portuguese, Indonesian for Malay.
3. A subtitle in the film’s original language.
4. English.
5. Otherwise, another language that has subtitles for the video.

The original language comes before English because it translated best when we measured it. In October 2026 we translated the same scenes of 5 films into 5 languages from different subtitles, 89 translations in all. For the films not made in English, the translation from the film’s original language was judged best in 13 of 13 cases by one judge and in 10 of 13 by the other. Every translation goes straight from that subtitle into your language, never through English, and a subtitle that a site marks as machine-translated is never used. For anime, the Japanese original comes from Jimaku when you add your own free Jimaku key.

Is it really free?

Yes. Subtitle Sync for Stremio is free and has no ads, and the translation runs on your own free Gemini API key from Google AI Studio: no card and no paid account.

• Google’s free plan has daily limits, which Google sets and can change. In October 2026 a free key allowed 500 requests a day for the model used, and one film or episode took 2 to 14 of them.
• A translation somebody already made is given to you without a key, as long as you get the same subtitle it was made from.
• When no site has any subtitle at all, a text subtitle track built into your video is translated instead. That needs your TorBox API key or your stream addon link from step 3 of the setup, because the addon has to read the file, and TorBox is a paid service.

Gemini or DeepL?

Either, or both. Gemini is free with no card, and its free limits come back every day. DeepL uses your own DeepL API key: a new DeepL account gets 1,000,000 characters once, about 19 films, with no card; older free DeepL accounts get 500,000 characters a month, and paid DeepL plans work too.

• With both keys you choose on the setup page which one translates first. When it cannot go on (its limit used up, its key refused, or busy), the other one takes over from where it stopped.
• A translation starts as soon as the subtitle list appears, so it also spends characters on subtitles you never open. With DeepL’s one-time characters you may prefer “Translate only when I pick the subtitle” in the advanced options.
• Translations made with DeepL are kept and offered to everyone, the same as Gemini’s.

Is the translated subtitle in sync with my video?

It is timed the same way as the subtitle it was translated from: lined up with your video’s own subtitle track when the addon can read it, or with an OpenSubtitles subtitle made for your file. A translation of the video’s built-in track has the video’s own timing.

The row says how it was timed, like every other row. In apps that show the row’s text it reads, for example, “✅ Synced to video · Machine translation from English”. Where the film begins with a pause, the subtitle shows “Machine translation (Gemini)” for a few seconds, or “(DeepL)” when DeepL made it. See why subtitles go out of sync for how the timing works.

How long does it take?

Usually less than a minute. Measured on the server in October 2026: an episode took 13 to 18 seconds, a long film of 1,578 lines about 40 seconds.

It starts when the subtitle list appears, before you pick anything, so it is often ready by the time you choose it. If it is not, the player shows how far along it is: choose the subtitle again a minute later. In the setup page's advanced options you can make it wait until you pick it instead, to save your free Gemini limit or your DeepL characters.

How to set it up

1. Open Google AI Studio at aistudio.google.com/apikey, sign in with your Google account and choose “Create API key”. Copy the key.
2. On the setup page, in step 2, tick “Translate a subtitle from another language with Gemini” and paste the key. The page checks that Google accepts it.
3. Optional: tick “Translate a subtitle from another language with DeepL” too, and paste your DeepL API key from your DeepL account (Account, API Keys). The page says how many characters it has left. With both, choose which one translates first.
4. Finish the setup and install. If Subtitle Sync for Stremio is already installed, uninstall the old one in Stremio first, then install the new one: Stremio keeps one addon per link, so a changed setup would show every subtitle twice.

What to know before you use it

• A machine translation can have mistakes, most often in names, jokes and slang. It is meant for videos that have no subtitle in your language at all.
• Only the subtitle’s text is sent to Google or DeepL, never your video, your file or your account. On Google’s free plan, Google may read and use what is sent to it, and it asks that you are 18 or older. On DeepL’s free plan, DeepL may keep the text it is sent.
• Your key is encrypted inside your addon link and never stored on the server.
• In the advanced options on the last step you can choose the Gemini model; Automatic (3.5 Flash Lite, then 3.1 Flash Lite) is the default.

A subtitle someone wrote, or an AI translation?

Setup takes 5 to 15 minutes on a guided page, in English, Serbian or Brazilian Portuguese. More answers or start now:

Start setup →