AI Subtitle Translator for the Video You Are Watching

An AI subtitle translator for files vs. on-page translation

A classic subtitle translator takes an existing .srt or .vtt file and rewrites its lines in another language. That is fast and accurate when you already have a good source file whose timing matches the version you are watching. The catch is the first step: you need the file, and for plenty of videos nobody has made one.

MiraiSub starts from the audio instead. Because it does not need a source subtitle, it can handle videos that have no captions at all. The price is an extra step, speech recognition, so the result depends on how clearly people speak in the recording. If you already have a matching subtitle file, translating that file is usually simpler and you do not need this extension.

What happens between pressing play and reading the line

The extension picks up the audio of the video on the page, a speech-to-text (STT) service converts the dialogue into text with timing, and a large language model (LLM) translates each line into the language you chose. The translated lines are shown in an overlay layer above the player, so the original page is left untouched.

Subtitles that have been generated once are kept in a shared cache so that the next viewer of the same video does not wait for the whole pipeline again. The cache is keyed by the video, not by who watched it.

• Pick the target language in the popup: Vietnamese, Indonesian, Spanish, English, Chinese, Korean, Thai, Portuguese, Japanese, Russian, French, German, Hindi, Arabic or Turkish.
• Works on pages that use a standard HTML5 video player.
• A free plan with a daily limit is available; paid plans raise it.

Where it helps most

Talks, lectures, interviews, product demos and documentaries in a language you read poorly are the obvious cases. The same goes for older recordings that were never captioned, and for clips shared in a chat without any subtitles. If you only need the gist of what is being said, reading a translated line while you watch is often enough.

It is also useful for language learners who want a second line of text next to what they hear, as long as they remember that the translation is machine-made and is not a teaching resource.

An honest note on accuracy

AI subtitles are not perfect. Loud background music, people talking over each other, whispering, heavy slang and names can produce recognition mistakes, and the translation inherits them. Jokes, wordplay and cultural references may be rendered too literally. Treat the output as a reading aid for understanding, not as a professional translation, and do not publish it without checking it yourself.

Timing is also approximate, and the delay before the first line appears depends on the length of the video and how busy the service is.

Limits you should know about before installing

MiraiSub does not host videos, does not give download links and does not export subtitle files; the text only exists on the page you opened. It runs on desktop Chromium-based browsers such as Chrome and Edge and does not work in mobile apps. Sites with a custom or protected player may not work, and the sites we have actually tested are listed on the supported sites page.

To try it, add the extension from the install page, open a video, choose the language in the popup and turn it on. The how-to page walks through the same steps.

• A video without any speech has nothing to translate.
• Subtitles burned into the picture stay where they are; the extension cannot remove them.
• Processing time varies with video length and current load.