Make a screenshot of a video.

_VideoScreenshot.md

Create a new bookmark and use this as the link:

javascript:(function()%7Bvar%20t%3Ddocument.querySelectorAll(%22video%22)%2Ce%3D%5B%5D%3Bfor(var%20a%20of%20t)a.paused%7C%7Ca.ended%7C%7Ce.push(a)%3Bvar%20n%3D0%3D%3D%3De.length%3Ft%3Ae%2Co%3Dnull%2Cr%3D0%3Bfor(var%20a%20of%20n)%7Bvar%20d%3Da.videoWidth*a.videoHeight%3Bd%3Er%26%26(o%3Da%2Cr%3Dd)%7Do%3Ffunction(t)%7Bvar%20e%3Ddocument.createElement(%22canvas%22)%3Be.width%3Dt.videoWidth%2Ce.height%3Dt.videoHeight%2Ccontext%3De.getContext(%222d%22)%3Bvar%20a%3Dnew%20Date%3Bcontext.drawImage(t%2C0%2C0%2Ct.videoWidth%2Ct.videoHeight)%3Bvar%20n%3De.toDataURL(%22image%2Fpng%22)%2Co%3Ddocument.createElement(%22a%22)%3Bo.href%3Dn%2Co.download%3D%22Screenshot_%22%2Ba.getFullYear()%2B%22_%22%2BString(a.getMonth()%2B1).padStart(2%2C%220%22)%2B%22_%22%2BString(a.getDate()).padStart(2%2C%220%22)%2B%22_%22%2BString(a.getHours()).padStart(2%2C%220%22)%2B%22-%22%2BString(a.getMinutes()).padStart(2%2C%220%22)%2B%22-%22%2BString(a.getSeconds()).padStart(2%2C%220%22)%2B%22.png%22%2Co.click()%7D(o)%3Aalert(%22No%20video%20found!%22)%7D)()

When you click that link a screenshot of the the biggest playing video is made (if none is playing then of the biggest loaded video). If now video is found you might need to view only the (i)frame of the video.

VideoScreenshot.js

javascript:(function() {
	function screenshot(video) {
		var canvas = document.createElement('canvas');
		canvas.width  = video.videoWidth;
		canvas.height = video.videoHeight;
		context = canvas.getContext('2d');
		var now = new Date();
		context.drawImage(video, 0, 0, video.videoWidth, video.videoHeight);
		var url = canvas.toDataURL('image/png');
		var link = document.createElement('a');
		link.href = url;
		link.download = 'Screenshot_'+
			now.getFullYear()+'_'+String(now.getMonth()+1).padStart(2, '0')+'_'+String(now.getDate()).padStart(2, '0')+'_'+
			String(now.getHours()).padStart(2, '0')+'-'+String(now.getMinutes()).padStart(2, '0')+'-'+String(now.getSeconds()).padStart(2, '0')+
			'.png';
		link.click();
	}

	var videos = document.querySelectorAll('video');
	var playing = [];

	for (var video of videos) {
		if (!video.paused && !video.ended) {
			playing.push(video);
		}
	}

	var selected = playing.length === 0 ? videos : playing;
	var biggestVideo = null;
	var maxArea = 0;

	for (var video of selected) {
		var area = video.videoWidth * video.videoHeight;
		if (area > maxArea) {
			biggestVideo = video;
			maxArea = area;
		}
	}

	if (biggestVideo) {
		screenshot(biggestVideo);
	} else {
		alert('No video found!');
	}
})();