JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li>http://www.youtube.com/watch?v=dw1Vh9Yzryo</li>
    <li>http://www.youtube.com/watch?v=bOF3o8B292U</li>
    <li>http://www.youtube.com/watch?v=yAY4vNJd7A8</li>
    <li>http://www.youtube.com/watch?v=yAY4vNJd7A8</li>
    <li>http://www.youtube.com/watch?v=dw1Vh9Yzryo</li>
    <li>http://www.youtube.com/watch?v=bOF3o8B292U</li>
    <li>http://www.youtube.com/watch?v=yAY4vNJd7A8</li>
    <li>http://www.youtube.com/watch?v=dw1Vh9Yzryo</li>
</ul>

JavaScript

var seen = {};
$('li').each(function() {
    var txt = $(this).text();
    if (seen[txt])
        seen[txt] += 1;
    else
        seen[txt] = 1;
});
newlist = $('<ul />');
for (var vid in seen) {
    $("<li>This video was repeated " + seen[vid] + " times and you can download it here: " + vid + "</li>").appendTo(newlist);
}
newlist.appendTo(document.body); // or wherever you want it