Control the YouTube player from the keyboard — seek, speed, volume and full screen. Same on every platform.
The keys that change how people watch are J, K and L — back ten seconds, play/pause, forward ten seconds — borrowed straight from professional video editors. The arrow keys nudge five seconds instead, which is handy for catching a moment you just missed. To get through a long video faster, Shift + > speeds playback up and Shift + < slows it down, stepping through YouTube's speed options.
A few single letters control the viewing experience: F toggles full screen, T switches to theater mode, I pops out the miniplayer so you can keep browsing, and C turns captions on or off. M mutes, and the up and down arrows handle volume. One caveat: the number keys 1 through 9 jump to 10% through 90% of the video — useful, but easy to hit by accident when you meant to type. For desktop browsing around the video, the Chrome shortcuts complement these.