let speed = 1

document.addEventListener('keypress', (ev) => {
	({
		"ArrowUp": () => {
			speed = Math.max(0, speed + 1)
		},
		"ArrowDown": () => {
			speed = Math.max(0, speed - 1)
		}
	})[ev.key]
})

setInterval(() => {
	const video = document.querySelector('video')[0]
	if (video.playbackRate !== speed) video.playbackRate = speed
}, 1000)