Shows the latency for a YouTube live stream.

youtube_show_latency.user.js

// ==UserScript==
// @name [YouTube] Shows latency.
// @description Shows latency.
// @match https://www.youtube.com/watch?v=*
// @namespace ynn
// ==/UserScript==

(function() {
    "use strict";

    function f() {
        const e_movie_player = document.querySelector('#movie_player');
        const e_date = document.querySelector('#date');
        if (e_movie_player === null || e_date === null) {
            window.setTimeout(f, 500);
        } else {

            if (document.querySelector('.view-count').innerText.endsWith('views')) {
                console.log('showLatency(): This is not a live stream. Exited.');
                return;
            } else {
                console.log('showLatency(): Started.');
            }

            const c = document.createElement('style');
            c.innerText = '.html5-video-info-panel { display: none; }';
            document.head.appendChild(c);

            e_movie_player.dispatchEvent(new Event('contextmenu'));
            document.querySelector('div.ytp-menuitem:nth-child(7)').click();

            const latency = document.querySelector('.html5-video-info-panel-content > div:nth-child(12) > span:nth-child(2) > span:nth-child(2)');

            const latency_display = document.createElement('yt-formatted-string');
            latency_display.classList.add('style-scope', 'yt-view-count-renderer');
            e_date.insertAdjacentElement('beforeend', latency_display);

            window.setInterval(() => {
                latency_display.innerText = `・Latency ${latency.innerText.replace(/.s/, 's')}`;
//                 latency_display.innerText = `・Latency ${latency.innerText}`;
            }, 1000);

        }
    }

    f();

})();