Separate the chats of different livestream events in a YouTube Live Chat history (as exported by Google Takeout) with buttons that embed the respective streams.

ytLiveChatTakeout.js

(d=>{
	const ce = n=>d.createElement(n), ac = (p,c)=>p.appendChild(c), an = (p,n)=>ac(p, ce(n))
	let p;
	[].forEach.call(d.querySelectorAll('li'), e=>{
		a = e.querySelector('a');
		if (!a || a.href == p) { return; }
		p = a.href;
		const t = ce('li'), b = an(an(e.parentNode.insertBefore(t, e), 'h1'), 'button')
		ac(b, document.createTextNode(p.split('?v=')[1]));
		b.addEventListener('click', ev=>b.outerHTML = '<iframe width=560 height=315 src=https://www.youtube.com/embed/' + b.textContent
			+ ' frameborder=0 allow="accelerometer;autoplay;clipboard-write;encrypted-media;gyroscope;picture-in-picture" allowfullscreen></iframe>')
	})
})(document)