Flashes larger words from subtitles, quick display of recent subtitles, translation to English and replay slow last 5sec
// ==UserScript==
// @name YouTube Language Learner Helper
// @namespace http://tampermonkey.net/
// @version 0.6
// @description Flashes larger words from subtitles, quick display of recent subtitles, translation to English and replay slow last 5sec
// @author James Stapleton
// @match https://www.youtube.com/watch*
// @match https://www.youtube.com/embed/*
// @grant none
// @license MIT
// ==/UserScript==
/*
Overview
This utility helps with learning a second language while watching YouTube videos in that language.
I’ve been learning Spanish primarily through the Comprehensible Input method, focusing on listening
and watching without English translations or subtitles. For more advanced content — especially podcasts
with few or no visual clues — I often missed parts of what’s said. I found myself pausing, checking subtitles,
sometimes looking up English translations, rewinding, or slowing down the speaker.
This script provides quick, convenient ways to do all of this. It also includes an auto-word flasher that helps
you pick up missed words without switching your brain into full “reading mode,” allowing you to remain
in "listening mode" while still following along.
Usage
[CC] must be available and enabled to work (script will try to enable automatically when loading a new page or video).
Ensure the subtitles are in your target language and not your native language.
Tested fine (in Brave w/Tampermonkey) on main YT site and embedded (dreaming spanish site), including when in full screen mode.
Autogenerated subtitles worked fine too.
Feature 1: Flash word helper
- It intercepts and hides the main subtitles, instead flashing up the longer words briefly on screen in random positions
- This feature is enabled by default
- Press '=' to toggle on/off flash words feature
- Press Shift+'=' to toggle through reducing frequency of flash words (red = max, green = 2/3 words show, blue = 1/3, else off)
Feature 2: Subtitle quick view
- Press ',' to bring up the most recent subtitles, closes after 2 seconds
Feature 3: Subtitle translation view
- Press '.' to bring up the most recent subtitles translated to English, closes after 2 seconds
Feature 4: Pause and show current subtitles
- Press ';' - remains pause and showing until you press ';' again
- While paused, you may also:
-- Press '.' to toggle between translated and untranslated
-- Press '[' and ']' to scroll back and forward through subtitle history
-- Note, if you resume with [space] or navigate using arrow keys, the translate window will remain, just hit ',' and it will clear in 2 secs
Feature 5: Slow replay with subtitles
- Press '-' key to replay last 5 seconds at 0.75x speed, subtitle text will also display for that duration
- If not far enough back, press '-' again. (Note slow play and subtitles will only last for 5 seconds from the last jump)
Feature 6: Saved word/phrases list
- When in paused Subtitle view, click on a word to select or hilight a phrase with mouse, then press 's'
- To view saved list, press Ctrl+'s'
*/
(function() {
'use strict';
let subtitlesRaw = ""; // store the continuously building subtitle text
let subtitlesRawPrior = "";
let subtitlesHistory = "";
let extractedOffsets = []; // track offsets for arrow navigation (sentence index)
let currentOffset = 0;
let overlay;
let flashTimeout;
let isTranslated = 0;
let flashWordsLevel = 0; // 0-3, 0 = max word show, 3 = flash none
/*
Appends an element to the fullscreen video container if it exists,
otherwise to the standard video player container, or fallback to body.
@param {HTMLElement} el - The element to append
*/
function appendToVideoContainer(el) {
const fullscreenElement = document.fullscreenElement;
const container = fullscreenElement || document.querySelector('.html5-video-player');
if (container) {
container.appendChild(el);
} else {
document.body.appendChild(el);
}
}
// Create overlay div
function createOverlay() {
overlay = document.createElement('div');
overlay.style.position = 'absolute';
overlay.style.top = '20%';
overlay.style.left = '50%';
overlay.style.transform = 'translateX(-50%)';
overlay.style.padding = '10px 20px';
overlay.style.background = 'rgba(0,0,0,0.7)';
overlay.style.color = 'white';
overlay.style.fontSize = '2vw';
overlay.style.fontFamily = 'sans-serif';
overlay.style.borderRadius = '10px';
overlay.style.display = 'none';
overlay.style.zIndex = '99999';
appendToVideoContainer(overlay);
}
function showOverlay(text) {
overlay.innerText = text;
overlay.style.display = 'block';
}
function hideOverlay() {
isTranslated = 0; // Reset so always default shows back
overlay.style.display = 'none';
}
// Intercept subtitles and hide YouTube's
function interceptSubtitles() {
function tryHook() {
const container = document.querySelector('.ytp-caption-window-container');
if (!container) {
setTimeout(tryHook, 1000);
return;
}
const subtitleObserver = new MutationObserver(() => {
const spans = container.querySelectorAll('.ytp-caption-segment');
if (spans.length > 0) {
const text = Array.from(spans).map(s => s.innerText).join(' ').trim();
if (text) {
subtitlesRawPrior = subtitlesRaw;
subtitlesRaw = text.trim(); // store full growing subtitle text
let newText = subtitlesRaw;
if (subtitlesRawPrior && newText.startsWith(subtitlesRawPrior)) {
newText = newText.slice(subtitlesRawPrior.length).trim();
}
subtitlesHistory += " " + newText;
subtitlesHistory = subtitlesHistory.slice(-500);
// build sentence offsets for navigation
extractedOffsets = subtitlesHistory.match(/[^.!?]+[.!?]*/g) || [];
// If no punctuation after a while, switch to auto-chunking
if (extractedOffsets.length === 1 && subtitlesHistory.length >= 20)
{
// No punctuation AND long enough → fallback to word chunking
const words = subtitlesHistory.trim().split(/\s+/);
const chunkSize = 10; // adjust as needed
extractedOffsets = [];
for (let i = 0; i < words.length; i += chunkSize) {
extractedOffsets.push(words.slice(i, i + chunkSize).join(" "));
}
}
currentOffset = extractedOffsets.length - 1; // point at last sentence
flashKeywords(newText);
}
spans.forEach(s => {
s.style.display = 'none'
});
}
});
subtitleObserver.observe(container, { childList: true, subtree: true });
console.log("✅ Subtitle observer hooked");
}
tryHook();
}
let debugContainer = document.createElement('div');
debugContainer.id = 'subtitleDebug';
debugContainer.style.position = 'fixed';
debugContainer.style.bottom = '10px';
debugContainer.style.right = '10px';
debugContainer.style.maxHeight = '200px';
debugContainer.style.overflowY = 'auto';
debugContainer.style.background = 'rgba(0,0,0,0.8)';
debugContainer.style.color = '#fff';
debugContainer.style.fontSize = '12px';
debugContainer.style.padding = '5px';
debugContainer.style.zIndex = 9999;
document.body.appendChild(debugContainer);
// Debug function
function debug(msg) {
const line = document.createElement('div');
line.textContent = msg;
debugContainer.appendChild(line);
// optional: auto-scroll to bottom
debugContainer.scrollTop = debugContainer.scrollHeight;
}
// Extract last N sentences capped at maxWords
function extractSentences(offset = currentOffset, maxWords = 20, maxSentences = 3) {
if (!extractedOffsets.length) return "";
let sentences = [];
let i = offset;
while (i >= 0 && sentences.length < maxSentences) {
sentences.unshift(extractedOffsets[i].trim());
i--;
}
let text = sentences.join(' ');
let words = text.split(/\s+/);
if (words.length > maxWords) {
text = words.slice(-maxWords).join(' ');
}
return text;
}
// Translation using LibreTranslate public endpoint
async function translateText(text, target = 'en') {
try {
const url = `https://translate.googleapis.com/translate_a/single?client=gtx&sl=auto&tl=${target}&dt=t&q=${encodeURIComponent(text)}`;
const res = await fetch(url);
if (!res.ok) throw new Error(`HTTP status: ${res.status}`);
const data = await res.json();
if (Array.isArray(data) && data[0] && Array.isArray(data[0][0])) {
return data[0].map(m => m[0]).join(' ');
}
throw new Error('Unexpected response format');
} catch (err) {
console.error('Translation failed:', err);
return '[Translation error]';
}
}
const keywordFlashState = {
activeFlashes: [],
maxFlashes: 5,
delay: 500 // ms between flashes
};
// Utility: pick random positions on screen
function randomPosition() {
const x = Math.random() * 80 + 10; // 10% to 90%
const y = Math.random() * 80 + 10;
return { x, y };
}
let lastExtractedWords = [];
// Function to extract keywords from a text
function extractKeywords(text, maxWords = 5) {
// Simple noun-ish extraction: take words longer than 3 letters
// Could be replaced with more advanced NLP
const words = text.match(/\p{L}{4,}(?:['’-]\p{L}+)*/gu) || [];
const uniqueWords = words.filter(word => !lastExtractedWords.includes(word));
lastExtractedWords = words;
return uniqueWords.slice(0, maxWords);
}
// Flash keywords
function flashKeywords(text) {
const keywords = extractKeywords(text, keywordFlashState.maxFlashes);
if (Math.random() <= flashWordsLevel / 3) {
return;
}
const levelColors = {
0: 'red',
1: 'green',
2: 'blue'
};
keywords.forEach((word, i) => {
setTimeout(async () => {
const div = document.createElement('div');
div.style.position = 'absolute';
div.style.left = randomPosition().x + '%';
div.style.top = randomPosition().y + '%';
div.style.background = 'rgba(0,0,0,0.7)';
div.style.color = levelColors[flashWordsLevel];
div.style.padding = '4px 8px';
div.style.borderRadius = '4px';
div.style.zIndex = 9999;
div.style.fontSize = '3vw';
div.style.display = 'block';
div.innerText = word;
appendToVideoContainer(div);
keywordFlashState.activeFlashes.push(div);
// Hide after 1 second
setTimeout(() => {
div.remove();
keywordFlashState.activeFlashes = keywordFlashState.activeFlashes.filter(d => d !== div);
}, 1000);
}, i * keywordFlashState.delay);
});
}
// Replay last X seconds in slow motion, keeping subtitles visible
function slowReplay(video, backSeconds = 5, speed = 0.75, durationMultiplier = 1.25) {
if (!video) return;
// Clear any previous timeout
if (window.replayTimeout) clearTimeout(window.replayTimeout);
// Skip back
video.currentTime = Math.max(0, video.currentTime - backSeconds);
// Slow playback
video.playbackRate = speed;
// Show current subtitle snippet
showOverlay(extractSentences());
// Schedule restoring normal speed & hiding overlay
const replayDuration = backSeconds * durationMultiplier * 1000;
window.replayTimeout = setTimeout(() => {
video.playbackRate = 1.0;
hideOverlay();
}, replayDuration);
}
let savedPhrases = [];
if (localStorage.getItem('YTLangLearnPhrases')) {
savedPhrases = JSON.parse(localStorage.getItem('YTLangLearnPhrases'));
}
async function saveSelection() {
const selection = window.getSelection().toString().trim();
if (!selection) return; // nothing selected
const dictPhrase = selection + " => " + await translateText(selection);
if (!savedPhrases.includes(dictPhrase)) {
savedPhrases.push(dictPhrase);
localStorage.setItem('YTLangLearnPhrases', JSON.stringify(savedPhrases));
console.log('Saved phrases:', savedPhrases);
}
}
function showSavedPhrases() {
const video = document.querySelector('video');
if (video && !video.paused) video.pause();
// Remove old popup if it exists
let oldPopup = document.getElementById('savedPhrasesPopup');
if (oldPopup) oldPopup.remove();
const popup = document.createElement('div');
popup.id = 'savedPhrasesPopup';
popup.style.position = 'fixed';
popup.style.top = '10px';
popup.style.right = '10px';
popup.style.width = '300px';
popup.style.height = '400px';
popup.style.backgroundColor = 'rgba(0,0,0,0.85)';
popup.style.color = 'white';
popup.style.padding = '10px';
popup.style.overflowY = 'auto';
popup.style.zIndex = 9999;
popup.style.borderRadius = '8px';
popup.style.fontFamily = 'sans-serif';
popup.style.fontSize = '14px';
// Button container
const btnContainer = document.createElement('div');
btnContainer.style.display = 'flex';
btnContainer.style.justifyContent = 'space-between';
btnContainer.style.marginBottom = '10px';
// Close button
const closeBtn = document.createElement('button');
closeBtn.textContent = '✖';
closeBtn.style.cursor = 'pointer';
closeBtn.onclick = () => popup.remove();
btnContainer.appendChild(closeBtn);
// Clear button
const clearBtn = document.createElement('button');
clearBtn.textContent = 'Clear List';
clearBtn.style.cursor = 'pointer';
clearBtn.onclick = () => {
if (savedPhrases.length === 0) {
alert('No saved phrases to clear.');
return;
}
const confirmed = confirm('Are you sure you want to clear all saved phrases?');
if (confirmed) {
savedPhrases = [];
localStorage.removeItem('savedPhrases');
alert('Saved phrases cleared.');
showSavedPhrases(); // refresh popup
}
};
btnContainer.appendChild(clearBtn);
popup.appendChild(btnContainer);
// Display saved phrases in reverse order
const reversed = [...savedPhrases].reverse();
reversed.forEach(phrase => {
const p = document.createElement('div');
p.textContent = phrase;
p.style.marginBottom = '5px';
popup.appendChild(p);
});
appendToVideoContainer(popup);
}
// Keyboard controls
function setupKeyHandlers() {
document.addEventListener('keydown', async (e) => {
const video = document.querySelector('video');
if (!video) return;
// ; = pause/resume
if (e.code === 'Semicolon') {
e.preventDefault();
if (video.paused) {
video.play();
hideOverlay();
} else {
video.pause();
showOverlay(extractSentences());
}
}
// [ = previous sentence
else if (video.paused && e.key === '[') {
e.preventDefault();
if (currentOffset > 0) {
currentOffset--;
showOverlay(extractSentences());
}
}
// ] = next sentence
else if (video.paused && e.key === ']') {
e.preventDefault();
if (currentOffset < extractedOffsets.length - 1) {
currentOffset++;
showOverlay(extractSentences());
}
}
// . = translate last extracted snippet
else if (e.key === '.') {
e.preventDefault();
if (extractedOffsets.length > 0) {
const snippet = extractSentences();
var text;
if (isTranslated == 0) {
isTranslated = 1;
text = await translateText(snippet);
} else {
isTranslated = 0;
text = snippet;
}
if (video.paused) {
showOverlay(text);
} else {
showOverlay(text);
clearTimeout(flashTimeout);
flashTimeout = setTimeout(hideOverlay, 2000);
}
}
}
// , = flash current snippet
else if (e.key === ',') {
e.preventDefault();
if (extractedOffsets.length > 0) {
showOverlay(extractSentences());
clearTimeout(flashTimeout);
flashTimeout = setTimeout(hideOverlay, 2000);
}
}
// - = rewind slower replay
else if (e.key === '-') {
e.preventDefault();
slowReplay(video, 5, 0.75, 1.5);
}
// = toggle flashWordsLevel
else if (e.key === '=') {
e.preventDefault();
if (flashWordsLevel == 3) {
flashWordsLevel = 0;
}
else {
flashWordsLevel = 3;
}
}
else if (e.key === '+') {
flashWordsLevel++;
if(flashWordsLevel == 4) flashWordsLevel = 0;
}
// 's' - saved phrases handling
else if (e.key === 's') {
e.preventDefault();
if (e.ctrlKey) {
showSavedPhrases();
}
else {
await saveSelection();
}
}
}, true);
}
function enableSubtitles() {
const ccButton = document.querySelector('.ytp-subtitles-button');
if (ccButton && ccButton.getAttribute('aria-pressed') === 'false') {
ccButton.click();
console.log("Subtitles turned ON");
return true;
}
return false;
}
// Keep trying until successful, give up after 10 seconds
let subtitlePressRetry = 10;
let subtitleInterval = setInterval(() => {
if (enableSubtitles() || (--subtitlePressRetry == 0)) {
clearInterval(subtitleInterval);
}
}, 1000);
const video = document.querySelector('video');
video.addEventListener('play', () => {
setTimeout(enableSubtitles, 500); // slight delay helps
});
function init() {
createOverlay();
interceptSubtitles();
setupKeyHandlers();
}
// Watch for SPA navigation
const pageObserver = new MutationObserver(() => {
if (document.querySelector('video') && !overlay) init();
});
pageObserver.observe(document.body, { childList: true, subtree: true });
})();