Tampermonkey: YouTube: show time left in title

youtube-time-left.tamper.js

// ==UserScript==
// @name         YouTube: show time left and channel in title
// @namespace    https://gist.github.com/vogler
// @downloadURL  https://gist.github.com/vogler/451aa48d0af7b659e391fdbeeea0d9d8/raw/youtube-time-left.tamper.js
// @version      0.11
// @description  YouTube: show time left and channel in title
// @author       Ralf Vogler
// @ match        https://www.youtube.com/watch?v=* // this will not work if you open youtube.com and then click on a video since it is a SPA
// @match        https://www.youtube.com/*
// @grant        none
// @noframes
// ==/UserScript==

'use strict';

// options
const opt = {
    onLoad: true, // false: only update title after video starts playing
    // position: 'start', // add to 'start' | 'end' of document.title -> just use start since it makes more sense
    withRate: true, // true: divide time left by playback speed, false: ignore playback speed
    stripNotifications: true, // remove leading number of notifications ('(123) ') from title
    watchedMark: ' ✔︎', // when < 10s left, show original duration + watchedMark
    withChannel: true,
}

const parseDuration = str => str.split(':').toReversed().reduce((a,x,i) => a + parseInt(x) * 60**i, 0); // to seconds
const formatDuration = seconds => new Date(1000 * seconds).toISOString().substr(11, 8).replace(/^[0:]+/, "");

const durationRegex = `(\\d{1,2}:)*\\d{1,2}(${opt.watchedMark})?`; // regex as string used below -> need to escape \
const durationTitleRegex = new RegExp(`^${durationRegex} `);

// meta-data for current video
const video = {
    title: document.title, // original title; without, if we open in background tab, document.title == 'YouTube' on first setTitle
    title2: undefined, // last title with duration we set via setTitle; used to undo YouTube's reset of title when leaving tab
    channel: {
        name: undefined,
        slug: undefined,
    },
    duration: undefined,
    playbackRate: undefined,
};

const setTitle = timeLeftSeconds => {
    let timeLeft = formatDuration(timeLeftSeconds);
    // console.log('youtube-time-left:', 'timeLeft:', timeLeft);
    if (timeLeftSeconds < 10) timeLeft = formatDuration(video.duration) + opt.watchedMark;
    let title = video.title.replace(durationTitleRegex, ''); // strip timeLeft: simpler and more reliable alternative to urlchange listener (requires @grant window.onurlchange) + MutationObserver on title
    if (opt.stripNotifications) title = title.replace(/^\(\d+\) /, '');
    if (opt.withChannel) {
        title = title.replace(/- YouTube$/, `[${video.channel.name}] - YouTube`); // ' - YouTube' still at end of title
        title = `${video.channel.slug}: ${title}`;
    }
    video.title2 = document.title = `${timeLeft} ${title}`;
};

(async function() {
    // window.addEventListener('focus', e => console.log('window.focus')); // to debug opening page in background tab

    // const v = document.querySelector('#movie_player video');
    // console.log('video:', v);
    // console.log('duration:', v.duration, 'playbackRate:', v.playbackRate);
    // duration is not set if page is loaded in background tab, playbackRate may still be 1 if Video Speed Controller extension runs afterwards

    // update time left in title
    // the surrounding MutationObserver is needed for when navigating from youtube.com to a video instead of opening it in a new tab
    (new MutationObserver((mutations, observer) => {
        if (document.location.pathname != '/watch') return; // not on a video page
        // if (!document.querySelector('#ytd-player')) return; // not enough since setting the title here will revert it to just 'YouTube'
        if (!mutations.some(m => m.target.className == 'ytp-large-play-button ytp-button')) return;
        // console.log(mutations);
        observer.disconnect(); // only need to attach listener once
        // if (document.title.match(durationTitleRegex)) return; // we can stop if the title has already been updated before
        const v = document.querySelector('#movie_player video'); // video element
        // console.log('video:', v);
        video.channel.name = document.querySelector('#channel-name')?.innerText; // e.g. 'Marques Brownlee'
        video.channel.slug = document.querySelector('#channel-name a').getAttribute('href').replace(/^\/@/, ''); // e.g. 'mkbhd'
        video.duration = parseDuration(document.querySelector('.ytp-time-duration').innerText);
        video.playbackRate = v.playbackRate; // this is only the initial rate, could update this below, but not currently used in title
        console.log('youtube-time-left:', video);
        const update = e => {
            if (document.location.pathname != '/watch') return;
            let timeLeft = (v.duration || video.duration) - v.currentTime;
            if (opt.withRate) timeLeft /= v.playbackRate;
            setTitle(timeLeft);
        };
        if (opt.onLoad) update();
        // v.addEventListener('timeupdate', update, { passive: true }); // getEventListeners($('video')).timeupdate.length was either 3 or 5 (before having observer.disconnect())
        v.ontimeupdate = update; // in any case, good to avoid attaching the same listener multiple times
    })).observe(document, { subtree: true, childList: true }); // more specific document.querySelector('#page-manager') and #content was not reliable

    // update title on soft navigation and undo YouTube's reset of title when leaving tab
    new MutationObserver((m, o) => {
        // console.log('youtube-time-left:', 'title changed:', document.title, 'from:', video.title2);
        if (document.title == 'YouTube') return;
        if (document.title.match(durationTitleRegex)) return; // new title already includes duration, i.e., we set it
        else if (video.title != document.title) { // update orgiginal title on soft navigation to new video
            console.log('youtube-time-left:', 'navigate to new title:', document.title, video.title2);
            video.title = document.title;
            video.title2 = undefined;
        }
        if (!video.title2) return; // title has not been updated yet; YouTube already sets the title 4 times before during load...
        console.log('youtube-time-left:', 'title changed by YouTube to:', document.title, 'from:', video.title2);
        document.title = video.title2; // undo reset of title using value from last setTitle
        // o.disconnect(); // doing this breaks title update for tabs opened in background
    }).observe(document.querySelector('title'), { childList: true }); // detects when title is changed
})();