yt-local/youtube/static/js/common.js

const Q = document.querySelector.bind(document);
const QA = document.querySelectorAll.bind(document);
const QId = document.getElementById.bind(document);
let seconds,
    minutes,
    hours;
function text(msg) { return document.createTextNode(msg); }
function clearNode(node) { while (node.firstChild) node.removeChild(node.firstChild); }
function toTimestamp(seconds) {
  seconds = Math.floor(seconds);

  minutes = Math.floor(seconds/60);
  seconds = seconds % 60;

  hours = Math.floor(minutes/60);
  minutes = minutes % 60;

  if (hours) {
    return `0${hours}:`.slice(-3) + `0${minutes}:`.slice(-3) + `0${seconds}`.slice(-2);
  }
  return `0${minutes}:`.slice(-3) + `0${seconds}`.slice(-2);
}

let cur_track_idx = 0;
function getActiveTranscriptTrackIdx() {
    let textTracks = QId("js-video-player").textTracks;
    if (!textTracks.length) return;
    for (let i=0; i < textTracks.length; i++) {
        if (textTracks[i].mode == "showing") {
            cur_track_idx = i;
            return cur_track_idx;
        }
    }
    return cur_track_idx;
}
function getActiveTranscriptTrack() { return QId("js-video-player").textTracks[getActiveTranscriptTrackIdx()]; }

function getDefaultTranscriptTrackIdx() {
  let textTracks = QId("js-video-player").textTracks;
  return textTracks.length - 1;
}

function doXhr(url, callback=null) {
    let xhr = new XMLHttpRequest();
    xhr.open("GET", url);
    xhr.onload = (e) => {
      callback(e.currentTarget.response);
    }
    xhr.send();
    return xhr;
}

// https://stackoverflow.com/a/30810322
function copyTextToClipboard(text) {
  let textArea = document.createElement("textarea");

  //
  // *** This styling is an extra step which is likely not required. ***
  //
  // Why is it here? To ensure:
  // 1. the element is able to have focus and selection.
  // 2. if element was to flash render it has minimal visual impact.
  // 3. less flakyness with selection and copying which **might** occur if
  //    the textarea element is not visible.
  //
  // The likelihood is the element won't even render, not even a
  // flash, so some of these are just precautions. However in
  // Internet Explorer the element is visible whilst the popup
  // box asking the user for permission for the web page to
  // copy to the clipboard.
  //

  // Place in top-left corner of screen regardless of scroll position.
  textArea.style.position = 'fixed';
  textArea.style.top = 0;
  textArea.style.left = 0;

  // Ensure it has a small width and height. Setting to 1px / 1em
  // doesn't work as this gives a negative w/h on some browsers.
  textArea.style.width = '2em';
  textArea.style.height = '2em';

  // We don't need padding, reducing the size if it does flash render.
  textArea.style.padding = 0;

  // Clean up any borders.
  textArea.style.border = 'none';
  textArea.style.outline = 'none';
  textArea.style.boxShadow = 'none';

  // Avoid flash of white box if rendered for any reason.
  textArea.style.background = 'transparent';


  textArea.value = text;

  let parent_el = video.parentElement;
  parent_el.appendChild(textArea);
  textArea.focus();
  textArea.select();

  try {
    let successful = document.execCommand('copy');
    let msg = successful ? 'successful' : 'unsuccessful';
    console.log('Copying text command was ' + msg);
  } catch (err) {
    console.log('Oops, unable to copy');
  }

  parent_el.removeChild(textArea);
}


window.addEventListener('DOMContentLoaded', function() {
    cur_track_idx = getDefaultTranscriptTrackIdx();
});

/**
 * Thumbnail fallback handler
 * Tries lower quality thumbnails when higher quality fails (404)
 * Priority: hq720.jpg -> sddefault.jpg -> hqdefault.jpg -> mqdefault.jpg -> default.jpg
 */
function thumbnail_fallback(img) {
    // Once src is set (image was loaded or attempted), always work with src
    const src = img.src;
    if (!src) return;

    // Handle YouTube video thumbnails
    if (src.includes('/i.ytimg.com/') || src.includes('/i.ytimg.com%2F')) {
        // Extract video ID from URL
        const match = src.match(/\/vi\/([^/]+)/);
        if (!match) return;

        const videoId = match[1];
        const imgPrefix = settings_img_prefix || '';

        // Define fallback order (from highest to lowest quality)
        const fallbacks = [
            'hq720.jpg',
            'sddefault.jpg',
            'hqdefault.jpg',
        ];

        // Find current quality and try next fallback
        for (let i = 0; i < fallbacks.length; i++) {
            if (src.includes(fallbacks[i])) {
                if (i < fallbacks.length - 1) {
                    img.src = imgPrefix + 'https://i.ytimg.com/vi/' + videoId + '/' + fallbacks[i + 1];
                } else {
                    // Last fallback failed, stop retrying
                    img.onerror = null;
                }
                return;
            }
        }
        // Unknown quality format, stop retrying
        img.onerror = null;
    }
    // Handle YouTube channel avatars (ggpht.com)
    else if (src.includes('ggpht.com') || src.includes('yt3.ggpht.com')) {
        const newSrc = src.replace(/=s\d+-c-k/, '=s240-c-k-c0x00ffffff-no-rj');
        if (newSrc !== src) {
            img.src = newSrc;
        } else {
            img.onerror = null;
        }
    } else {
        img.onerror = null;
    }
}