Each player has its own control: the native HLS interstitials client, or this demo’s library with the capabilities it is configured with. There is no ad presentation server behind this page. The capabilities travel on every asset-list request, as such a server would read them, and the answer is one static file per break that always carries every option of the ad. What decides what is drawn is the library: it keeps the first option the device can show and, when none fits, plays the break’s linear default or skips it. The combination is in the URL.