A quick gist to prevent websites from automatically playing videos.

fuck-off-autoplay.user.js

// ==UserScript==
// @name         Fuck Off Autoplay
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Videos with audio shouldn't be allowed to play without a user gesture.
// @author       eth-p
// @match        http://*/*
// @match        https://*/*
// @grant        none
// @downloadURL  https://gitcdn.xyz/cdn/eth-p/dc1745cd0b377e17c72d02c92d01ea3a/raw/fuck-off-autoplay.user.js
// ==/UserScript==

(function() {
    'use strict';

    // Environment.
    const DBG = (...args) => console.log(`[FOA] ${args[0]}`, ...args.slice(1));
    const SYM = Symbol('Fuck Off Autoplay');

    let mouse = {x: null, y: null};

    function onInteract(event) {

        mouse = {x: event.clientX, y: event.clientY};
    };

    function interacted(target) {
        for (const rect of target.getClientRects()) {
            if (
                (mouse.x > rect.left && mouse.x < rect.right) &&
                (mouse.y > rect.top  && mouse.y < rect.bottom)
            ) {
                return true;
            }
        }

        return false;
    }

    window.addEventListener('mousedown', onInteract);


    // Hook the play() method.
    const playVideo = HTMLVideoElement.prototype.play;
    HTMLVideoElement.prototype.play = function(...args) {
        if (this[SYM] || interacted(this)) {
            this[SYM] = true;
            playVideo.apply(this, args);
        } else {
            DBG("Prevented autoplay.", this);
        }
    }

    DBG("Loaded.");
})();