Convert Twitch VOD timestamps to local time, and adds a display that shows the local time for given point in the VOD.

twitch_vod_local_timestamps.js

// [INSTRUCTIONS]
// Read through this and make sure it's safe to run!
// Set the "vodStart" date to the time the VOD started.
// Paste and run it in your browser console (ctrl+shift+i) on the twitch VOD.

(() => {
  // [CHANGE THIS]
  // Set this string to the start time of the VOD (try using an "I'm live!" tweet to get an accurate time for this).
  let vodStart = new Date(1613241580000); // new Date(Date.parse("5:39:40 AM Feb 14 2021"));

  // [DO NOT CHANGE BELOW]
  clearInterval(window.lucaID);

  function format(n) {
    return String(n).padStart(2, "0");
  }
  
  function convertElTime(el) {
    let ns = el.textContent.split(":").map(s => Number(s));
    let hours,mins,seconds;
    if (ns.length === 2) {
      hours = 0;
      [mins, seconds] = ns;
    } else {
      [hours, mins, seconds] = ns;
    }
    let d = new Date(vodStart.getTime() + (seconds + mins * 60 + hours * 3600) * 1000);
    return `${format(d.getHours())}:${format(d.getMinutes())}:${format(d.getSeconds())}`;
  }

  let currentVodTimeEl = document.querySelector("[data-a-target='player-seekbar-current-time']");
  let listEl = document.querySelector(".video-chat__message-list-wrapper").firstElementChild.firstElementChild;

  let currentTimeEL = document.getElementById("luca-vod-time");
  if (!currentTimeEL) {
    currentTimeEL = document.createElement("div");
    currentTimeEL.id = "luca-vod-time";
  }
  currentTimeEL.style.cssText = "z-index: 9999; position: absolute; top: 0; padding: 4px; background: #181818; border: 1px solid #404040; font-size: 150%;";
  document.body.append(currentTimeEL);

  window.lucaID = setInterval(() => {
    // Set local time element from VOD time.
    currentTimeEL.textContent = convertElTime(currentVodTimeEl);

    // Convert chat timestamps to local time.
    for (let el of listEl.children) {
      if (!el.dataset.ts) {
        el.dataset.ts = "1";
        let tse = el.querySelector("button p");
        tse.textContent = convertElTime(tse);
      }
    }
  }, 500);
})();