So it turns out the “YouTube voice” is just a vari­ety of ways of empha­siz­ing words, none of which are actu­al­ly exclu­sive to YouTube—people employ these devices in speech all the time. But they gen­er­al­ly do it to grab the listener’s atten­tion, and when you’re just talk­ing to a cam­era with­out much action, it takes a lit­tle more to get, and keep, that atten­tion.