a given URL is the access location for the source files for the library

My task was to merge two videos together and play them one after another automatically.
This is the source code of my project
html code –

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>video js</title>
    <link rel="stylesheet" href="index.css">
</head>
<body>
    <video id="videoPlayer" width="500" height="350" controls style="background:black">
        <source class="current" src="MY_VIDEO.mp4" type="video/mp4" />
        <source src="video2.mp4" type="video/mp4" />
      </video>
    <script src="script.js"></script>
</body>
</html>

script code –


var video = document.getElementById('videoPlayer');

video.addEventListener('ended', function(event) {
  var currentVid = document.querySelector("#videoPlayer source.current");
  var nextVid = document.querySelector("#videoPlayer source.current + source") || document.querySelector("#videoPlayer source:first-child");
  
  currentVid.className = "";
  nextVid.className = "current";
  
  video.src = nextVid.src;
  video.play();
});

My next task says https://videojs.com/ is the URL to access the source files for the library.
I am not getting what does this means?
Any idea?
Thanks in advance 🙂