As someone who frequently watches videos, changing the tempo is very underrated, as there's usually no good reason to waste time watching people talk at their natural speed. I used to do this with VLC (it can stream YouTube), but YouTube's HTML5 player now implements tempo adjustment as well, and I use the ImprovedTube Chrome extension to set the tempo to 1.5x by default. It can be conveniently changed with the keyboard as well (Ctrl+< and Ctrl+>). Discovering this has been a game changer with regard to watching technical videos.