LocalSub - YouTube Local AI Subtitles & Translate

Stop uploading your audio just to read it back. Most YouTube subtitle extensions send your video URL or your audio to a server, log your activity, lock features behind a sign-in, or stop working the moment you go offline. If you watch tutorials, lectures, dev talks, or foreign-language content every day, that adds up — to dependency, to slowdowns, and to a privacy tradeoff you never agreed to. LocalSub takes a different path. The transcription model and the translation model both run inside your browser, on your machine. Your audio never leaves Chrome. WHY YOUTUBE SUBTITLES ARE HARDER THAN THEY LOOK YouTube has captions for many videos, but the experience is patchy: - The CC track is in the wrong language - Auto-generated captions are noisy and untranslated - The video has no captions at all (common for new uploads, podcasts, screencasts) - The official translation drops technical terms and proper nouns - You want a clean SRT or TXT file for note-taking, but the page only shows the text as an overlay - You want the original and the translation side by side, not just one of the two Most tools solve part of this and create new problems — they require an API key, they upload your audio to an unknown server, they force a paid plan after a few videos, or they break whenever YouTube changes a player script. LocalSub is built to solve all of it in one panel without sending the audio anywhere. WHAT THIS EXTENSION DOES LocalSub adds a side panel to YouTube that does three things, in this order. It reads YouTube's existing captions when they exist, including auto-generated ones, directly from the player. If there is no caption track, it transcribes the audio locally with Whisper — the same open speech model used in many serious transcription tools — running fully inside your browser via WebAssembly. It then translates every segment into the target language you picked, using NLLB-200, a 200-language model from Meta AI Research that also runs locally. When the model cannot fit in memory on a smaller device, the panel automatically falls back to a free public translation endpoint so the workflow never dead-ends. Here is what you get: Local Whisper transcription — works on videos with no captions, no signed audio token, and no third-party transcription service. Local NLLB-200 translation — 19 target languages including English, German, French, Spanish, Italian, Portuguese, Dutch, Russian, Polish, Turkish, Arabic, Japanese, Korean, Simplified and Traditional Chinese, Hindi, Thai, Vietnamese, and Indonesian. Side-panel UI — keeps the video where it is and the transcript where it belongs, in a column you can read while the video plays. Clickable transcript — every segment is a timestamp; click it and the video seeks to that moment in the source tab. Bilingual rendering — by default each segment shows the translated line on top and the original line below it, so you can match the translation to the source word-for-word. SRT export — produces a standard subtitle file you can drop into VLC, Premiere, DaVinci Resolve, or anywhere else. TXT export — produces a clean reading transcript without timestamps, useful for note apps, AI chats, or sharing. Export mode selector — one tap switches between bilingual, translation only, or original only, for both SRT and TXT. 14 UI locales — the panel itself speaks English, Simplified Chinese, Traditional Chinese, Japanese, Korean, German, French, Spanish, Brazilian Portuguese, Italian, Arabic, Dutch, Russian, and Turkish. HOW IT WORKS 1. Open any video on youtube.com. 2. Pick your target language in the side panel — you only do this once. 3. Click Transcribe + Translate beside the video title. 4. Wait for the pipeline — fetching, transcribing if needed, translating. 5. Read the transcript, click any line to jump to that moment, or export to SRT or TXT. That is the whole loop. There is no account to create and no API key to paste. The first 5 videos each day are free; see the Pricing section below if you want the cap removed. WHY A SIDE PANEL INSTEAD OF A POPUP Popups vanish the moment you click anywhere else, which is exactly what you do when you scrub the video, change tabs, or open the description. A side panel stays open, shares the same window as the video, and gives the transcript enough vertical space to be readable without truncation. It also lets you copy a long line without the panel closing under your cursor. EXPORT MODES IN DETAIL BILINGUAL — both lines per segment. Useful for language learners and translators who need to verify the translation against the source. TRANSLATION — only the target language. Useful for clean reading and for handing the SRT to a player that does not support multi-line styling. ORIGINAL — the source language only. Useful when the video already has good captions and you just want a clean SRT or TXT, with no AI rewriting. The active mode applies to both SRT and TXT export, so you do not have to switch twice. REAL SCENARIOS WHERE THIS HELPS Watching a 90-minute Korean dev talk that only has Korean auto-captions: LocalSub reads the Korean track from the player, translates every line into your language, and lets you click your way back to the moments that matter. No upload, no waiting in someone's queue. Following a German university lecture with no captions at all: The page has no CC track. LocalSub reaches into the audio, runs Whisper on your machine, and produces timestamped segments. You then export SRT and load it into your player of choice. Studying a Japanese podcast clip embedded on YouTube: You want bilingual subtitles to read along. LocalSub transcribes the Japanese, translates to English, and exports a bilingual SRT. You drop it into VLC and watch with both rails. Skimming a four-hour course in English in your native language: You only have time for the highlights. LocalSub gives you a clickable transcript in the side panel; you scan, you click, you watch the relevant 30 seconds, you mo…