An HTTP request has to be sent on each tracker for each video to spy. If we want to spy all PeerTube's videos, we have to send as many requests as there are videos (so potentially a lot)
<x id="START_TAG_STRONG" ctype="x-strong" equiv-text="<strong>"/>Subscribe<x id="CLOSE_TAG_STRONG" ctype="x-strong" equiv-text="</strong>"/> to channels to be notified of new videos