Adds keyboard shortcuts to HTML5 videos.

Add video keyboard shortcuts.user.js

// ==UserScript==
// @name         Video keyboard shortcuts
// @namespace    https://github.com/buzamahmooza
// @version      0.5
// @description  Adds keyboard shortcuts to HTML5 videos.
//               Left Click:  Toggle Pause/Play
//               F or dblClk: Toggle Fullscreen
//               SpaceBar:    Toggle Pause/Play
//               Left/Right:  Navigate back/forward
//               -,[ / =,]:   - / + Playback speed
//               Zero (0):    Reset playback speed
// @author       Faris Hijazi
// @match        *
// @include      *
// @updateURL    https://gist.github.com/buzamahmooza/b940c84b16f0b5719fa994d54c785cab/raw/
// @grant        GM_setValue
// @grant        GM_getValue
// ==/UserScript==

const alwaysFastPlayBack = true;
var vids = document.getElementsByTagName('video');
if(!vids) {console.log('No videos found.'); return;}

function observeDocument(callback) {
	callback(document.body);
	new MutationObserver(function(mutations){
		for (var i = 0; i < mutations.length; i++) {
			if (!mutations[i].addedNodes.length) continue;
			callback(mutations[i].target);
		}
	}).observe(document.body, {
		childList: true, subtree: true,
		attributes: false, characterData: false
	});
}
// observeDocument(go);
go();
function go(){
	for(var i=0; i<vids.length ;i++)
	{
		var vid = vids[i];
		var getVideo = function(){return vid; };

		if(alwaysFastPlayBack)
			vid.playbackRate = GM_getValue('startingPlaybackRate', 1.7);

		console.log('Found video: '+vid.src+'\nAdding video shortcuts.');
		// keyboard listener
		document.addEventListener('keydown', function(e) {
			let vid = getVideo();
			if (!e.shiftKey && !e.ctrlKey && !e.altKey && !e.metaKey) {
				switch(e.keyCode){
					case 221: // (])
					case 187: // (=)
						vid.playbackRate+=0.1;
						e.preventDefault();
						savePlaybackRate(vid.playbackRate);
						break;
					case 219: // ([)
					case 189: // (-)
						vid.playbackRate-=0.1;
						e.preventDefault();
						savePlaybackRate(vid.playbackRate);
						break;
					case 48: // Alpha 0 (zero)
						vid.playbackRate = 1;
						console.log('reset playback speed');
						savePlaybackRate(vid.playbackRate);
						break;
					case 70: // F
						//Full screen
						toggleFullScreen();
						// getVideo().webkitEnterFullScreen();
						console.log('Full screen');
						break;
				}
				if(!/youtube.com/.test(document.location.href)) // skip this listener for youtube
					switch(e.keyCode){
						case 75: // K
						case 32: //Space bar
							if(vid.paused)
								vid.play();
							else
								vid.pause();
							e.preventDefault();
							break;
						case 76: // L
						case 39: // RightArrow
							vid.currentTime+=10;
							e.preventDefault();
							break;
						case 74: // J
						case 37: // LeftArrow
							vid.currentTime-=10;
							e.preventDefault();
							break;
						case 38: // UpArrow
							vid.volume+=0.1;
							e.preventDefault();
							break;
						case 40: // DownArrow
							vid.volume-=0.1;
							e.preventDefault();
							break;
					}
			}
		},false);

		if(/youtube.com/.test(document.location.href)){
			console.log("Skipping mouse listener in video cuz it's youtube");
			continue; // don't run on youtube (ruins the click functions)
		}
		// mouse click listener
		getVideo().addEventListener("click", function(){
			console.log('clicked on video');
			var vid = document.querySelector('video');
			if(vid.paused)
				vid.play();
			else
				vid.pause();
		});
		// mouse dblclick listener
		var isFullScreen;
		getVideo().addEventListener("dblclick", function () {
			console.log('double click');
			toggleFullScreen();
		}, false);
		var toggleFullScreen = function(){
			if(!isFullScreen) {
				getVideo().webkitEnterFullScreen();
				isFullScreen = true;
			} else {
				getVideo().webkitExitFullScreen();
				isFullScreen = false;
			}
		};
	}

}
function savePlaybackRate(newPlaybackRate){
	if(newPlaybackRate)
		GM_setValue('startingPlaybackRate', newPlaybackRate);
}

//     console.log('Videos found:');
//     for(var j=0; j< vids.length ;j++){
//         console.log(vids[j].src);
//         console.log(vids[j].outerHTML);
//     }

Description

Adds keyboard shortcuts to HTML5 videos.

• Left Click on video / SpaceBar: Toggle Pause/Play
• Left/Right: Navigate back/forward
• ( - ) : Decrease playback speed
• ( = ) : Increase playback speed

How to use

You need to add a userscript browser extension for this to work.
Two examples are TamperMonkey or GreaseMonkey.
Download once you've added one, click this link the RAW link and it should be added to your userscript extension.
Enjoy :)