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YouTube - Remaining Time Indicator

Displays the remaining duration of a YouTube video next to the video duration, taking into account the playback rate.

// ==UserScript==
// @name                          YouTube - Remaining Time Indicator
// @name:fr                       YouTube - Indicateur du temps restant
// @name:es                       YouTube - Indicador de tiempo restante
// @name:de                       YouTube - Anzeige der verbleibenden Zeit
// @name:it                       YouTube - Indicatore del tempo rimanente
// @name:zh-CN                    YouTube - 剩余时间指示器
// @namespace                     https://gist.github.com/4lrick/cf14cf267684f06c1b7bc559ddf2b943
// @version                       2.0
// @description                   Displays the remaining duration of a YouTube video next to the video duration, taking into account the playback rate.
// @description:fr                Affiche la durée restante d'une vidéo YouTube à côté de la durée de la vidéo, en tenant compte de la vitesse de lecture.
// @description:es                Muestra la duración restante de un video de YouTube junto a la duración del video, teniendo en cuenta la velocidad de reproducción.
// @description:de                Zeigt die verbleibende Dauer eines YouTube-Videos neben der Videodauer an und berücksichtigt dabei die Wiedergabegeschwindigkeit.
// @description:it                Mostra la durata rimanente di un video di YouTube accanto alla durata del video, tenendo conto della velocità di riproduzione.
// @description:zh-CN             在视频时长旁边显示YouTube视频的剩余时长，考虑播放速度。
// @author                        4lrick
// @match                         https://www.youtube.com/*
// @icon                          https://www.google.com/s2/favicons?sz=64&domain=youtube.com
// @grant                         none
// @license                       GPL-3.0-only
// ==/UserScript==

(function() {
    'use strict';
    let timeDisplay;
    let lastPlaybackRate = null;
    let lastRenderedText = '';
    let lastCurrentTime = null;

    function createTimeDisplayElement() {
        const timeDisplayElement = document.createElement('span');

        timeDisplayElement.style.display = 'inline-block';
        timeDisplayElement.style.marginLeft = '10px';
        timeDisplayElement.style.color = '#ddd';

        return timeDisplayElement;
    }

    function displayRemainingTime() {
        const videoElement = document.querySelector('video');
        const isLive = document.querySelector('.ytp-time-display')?.classList.contains('ytp-live');
        const miniplayerUI = document.querySelector('.ytp-miniplayer-ui');
        const isMiniplayerVisible = miniplayerUI && getComputedStyle(miniplayerUI).display !== 'none';
        const currentTime = videoElement?.currentTime;
        const timeContainer = document.querySelector(
            isMiniplayerVisible ? '.ytp-miniplayer-ui .ytp-time-contents' : '.ytp-chrome-controls .ytp-time-contents'
        );
        const shouldUpdate =
            videoElement &&
            !isLive &&
            (
                !videoElement.paused ||
                videoElement.playbackRate !== lastPlaybackRate ||
                currentTime !== lastCurrentTime
            );

        if (!videoElement || isLive || !timeContainer) {
            if (timeDisplay) {
                timeDisplay.remove();
                timeDisplay = null;
            }
            requestAnimationFrame(displayRemainingTime);
            return;
        }

        if (!timeDisplay) {
            timeDisplay = createTimeDisplayElement();
            timeContainer.appendChild(timeDisplay);
        }

        if (!timeContainer.contains(timeDisplay)) {
            timeDisplay.remove();
            timeContainer.appendChild(timeDisplay);
        }

        if (shouldUpdate) {
            const timeRemaining = (videoElement.duration - videoElement.currentTime) / videoElement.playbackRate;
            const hours = Math.floor(timeRemaining / 3600);
            const minutes = Math.floor((timeRemaining % 3600) / 60);
            const seconds = Math.floor(timeRemaining % 60);
            const text = `(${hours > 0 ? `${hours}:` : ''}${minutes.toString().padStart(2, '0')}:${seconds.toString().padStart(2, '0')})`;

            if (text !== lastRenderedText) {
                timeDisplay.textContent = text;
                lastRenderedText = text;
            }

            lastPlaybackRate = videoElement.playbackRate;
            lastCurrentTime = currentTime;
        }

        requestAnimationFrame(displayRemainingTime);
    }

    function initRemainingCounter() {
        const timeContainer = document.querySelector('.ytp-time-contents');

        if (timeContainer) {
            timeDisplay = createTimeDisplayElement();
            timeContainer.appendChild(timeDisplay);
            requestAnimationFrame(displayRemainingTime);
            observer.disconnect();
        }
    }

    function checkVideoExists() {
        const videoElement = document.querySelector('video');

        if (videoElement) {
            initRemainingCounter();
        }
    }

    const observer = new MutationObserver(checkVideoExists);
    observer.observe(document.body, { childList: true, subtree: true });
})();