I myself use MySpeed. It costs 29$ but you don’t have to download the video and can change the playback speed from 0.3 to 3.0. There are probably equivalent programs for free, but my google-fu wasn’t strong enough to find them.
You can use mplayer or vlc to stream youtube videos and they have the ability to change playback speed.
You can use mplayer or vlc to stream youtube videos and they have the ability to change playback speed.