This Chrome extension adds a speed adjustment slider attached to the left edge of the video window on all pages from the youtube.com domain. The primary motivation for this extension is to adjust videos to the user's individual auditory processing rate, which, for a particular subject matter, may be faster or slower than the speed of the video, depending on the user.
Auditory processing speed is the speed at which your brain can understand and truthfully encode into memories a stream of information being processed through the auditory system (the rate at which you can stuff information into your head through your ears).