The link to the impression pixel is needed to count impressions, if you want to collect it. The player will send this request when the ad starts playing. The click-through link is required if the ad is clickable.
The skipoffset parameter allows you to configure the ad skip button (in the example, 5 seconds).
You can generate the ad code dynamically from your server, changing the links depending on the situation. This is called ad rotation. For example, the advertising XML generates your script at site.com/vast/preroll.php?id=[id] - this address you specify in the player settings as an advertising link. To manage ads on different pages, just specify the vast_replace parameter in the player code.
var player = new Playerjs({id:"player", file:"https://site.com/video.mp4", vast_replace:{"[id]":1}});
In this example, the request will go to site.com/vast/preroll.php?id=1
Wrappers
A wrapper is an intermediate document that forwards the request to another VAST. At the same time, it can contain a full set of its own pixels, which will work out at the right time. The minimal wrapper looks like this: