Any language.
Understood live.
Real-time dual-language subtitles for live streams, videos and Netflix.
Translate any web page into your language, side by side.
Everything, in 46 seconds.
Plays muted on a loop. Tap the button in the corner to hear the narration.
Subtitles when there are some. Your ears when there aren’t.
When a video has subtitles, Simulcap translates the subtitle file the player already loads — the whole episode at once, cached so rewatching costs nothing. For live streams and videos without subtitles, it listens to the tab’s audio, recognizes the speech on your computer, and an AI model segments and translates it.
- Translation 1.5–2.5 s after the speaker pauses — accuracy first, without letting the delay run away
- Any language pair: pick both the source and the target; the spoken language is detected automatically
- Speech is recognized on your own computer and never uploaded
- Japanese → English
- Chinese → English
- Korean → English
- English → Japanese
- English → Chinese
- Any language pair
segment · correct · translatethe service you choose
Accurate, down to the jargon.
Not sentence-by-sentence literal translation. The AI model reads each line in context: misheard words are fixed, industry terms come out the way professionals say them, and hedges like “may” or “可能” keep their weight.
- Right even when misheard: recognition errors corrected from context
- Jargon in the industry’s own words: finance and tech terms follow your glossary
- Dramas read in context: names and forms of address stay consistent; omitted words are inferred from the scene
- Deep analysis (optional): a second pass refines each passage and replaces the live translation
Picture, sound and subtitles, in sync.
Recognition and translation take a moment. Turn on delayed playback and the picture and sound shift back a few seconds, so each subtitle appears the instant the speaker starts talking — like watching a broadcast with a short delay. Bluetooth headphone latency is compensated automatically.
- Set the delay yourself, or turn it off
- DRM-protected video that can’t be delayed simply plays in real time
Three subtitle styles.
Switch any time from the player menu, and adjust size, color, background and position to taste.
Live
Translates and refines as it goes, like rolling TV captions: the new line appears at the bottom, older lines move up and fade.
Professional terms, kept consistent.
Simulcap picks a glossary that fits the video and translates names and terms exactly the way you define them. A Fed glossary (English → Chinese) ships as an example; build your own for any field and language pair, or import one from a spreadsheet.
- Glossary terms also boost speech recognition, so names are heard correctly
- Dramas are read through once so names and titles stay consistent
- Add your own translation rules
見込み / 可能性 / may, never turn a forecast into a certainty, and write numbers as “0.25 percentage points”.Translates the pages browsers skip.
Many dashboards, consoles and online docs tell the browser “don’t translate”. In split-pane pages the right side often stays untranslated, and translated links stop working. Simulcap translates pages in any language into yours without changing a single character of the original — translations are added alongside, and one click brings the original back.
- Pages marked “do not translate”: single-page apps, cloud consoles and online docs still get translated
- Split panes and frames: two-pane router admin pages keep translating as you navigate
- Links, buttons and menus still work after translation, submenus included
- Layout stays intact: short labels get the translation beside them, paragraphs get a new line, tight buttons get smaller text
- Side by side or translation only, switch with ⌥A / Alt+A; text boxes are translated too
- Select to translate: tap the icon or right-click — or turn on “Translate on select” to see it instantly; the card matches the page’s light or dark colors
Example: a Japanese router admin with split panes, marked “do not translate”
Questions
More details in the README.
Which sites does it work on?
- YouTube
- Auto-generated and uploaded subtitles are translated directly; live streams and videos without subtitles are translated from the audio.
- Netflix
- Picks the original-language subtitles automatically — watch Japanese dramas and anime with English translations; falls back to audio when there are none.
- bilibili
- Uploader and AI subtitles (AI subtitles require signing in); otherwise the audio track is recognized in chunks and the first line appears within seconds.
- U-NEXT
- Audio only — see below.
- Any web page
- Translate the page (side by side or translation only) and translate selected text.
How do I install it?
Simulcap is still being polished. It will be published on the Chrome Web Store when it’s ready — one click to install, nothing technical.
What does it cost?
The extension is free. Translation uses your own API key. Estimated for one hour of continuous speech (about 400K input and 30K output tokens):
| Service | Default model | Input / output (per 1M tokens) | Per hour |
|---|---|---|---|
| Zhipu | glm-4.7-flash | Free | $0 |
| Google / Bing machine translation | web translation | Free | $0 |
| Qwen (Alibaba Cloud) | qwen-flash | ¥0.15 / ¥1.5 | $0.015 |
| Volcano Ark | doubao-seed-1.6-flash | ¥0.15 / ¥1.5 (unverified) | $0.015 |
| DeepSeek | deepseek-flash | $0.15–0.30 / $0.60–1.20 | $0.08–0.16 |
| Google Gemini | gemini-3.1-flash-lite | $0.25 / $1.50 | $0.15 |
| OpenAI | gpt-5-mini | $0.25 / $2.00 | $0.16 |
| Anthropic | claude-haiku-4-5 | $1.00 / $5.00 | $0.55 |
List prices as of October 2026 (US$1 ≈ ¥7.1). Subtitle files are translated once per episode and cached; local speech recognition and voice-over are free; “Deep analysis” uses several times more.
What do I need for audio translation?
Audio translation uses the speech-recognition service that comes with the extension. The first start installs it and downloads about 1 GB of models; after that, just leave it running. Not needed if you only translate subtitle files. Cloud recognition (Deepgram, with your own key) also works.
Which languages are supported?
Any pair. Choose both the source and the target language — Japanese, Chinese or Korean into English, English into Japanese, and anything else the AI model can translate; web pages work the same way. When listening, the spoken language is detected automatically: English and Japanese have dedicated speech models, other languages use a multilingual model. Recognition engines, translation models and languages are all extensible. The extension’s menus are available in English, 日本語 and 中文.
Is my data uploaded?
There is no Simulcap server and no data collection. Your keys stay in your browser and go only to the service you choose; scripts on video pages can’t read them. Audio is recognized locally and never stored. Web page text is sent to the translation service only after you click “Translate this page” or select text. Diagnostic logs are off by default.
Why is U-NEXT audio-only?
U-NEXT burns subtitles into the video picture, so there is no subtitle file to read; the picture is DRM-protected and can’t be delayed, so subtitles trail the audio by 1–2 seconds.
Free Google / Bing translation versus an AI model?
Machine translation works one sentence at a time without context, so deep analysis, consistent names and look-ahead context are unavailable. For AI quality at no cost, choose Zhipu.
What translates web pages, and does it cost anything?
Free Google translation by default — no key needed. You can switch to an AI model (DeepSeek, Zhipu and others) separately from the one used for video subtitles. Text is sent only when you click “Translate this page” or select text.
Which pages can’t be translated?
Pages embedded from another site (cross-origin frames) can’t be read by the browser; text drawn on a canvas or inside images has nothing to translate; code editors are skipped on purpose so code isn’t altered. Everything else — single-page apps, online docs, split panes, web components — works.
Can I use it with other subtitle-translation extensions?
Not recommended. Extensions like these all intercept the player’s subtitle requests and hide the native subtitles; running two at once makes them interfere. Turn the others off while using Simulcap.