I simply use mplayer and javascript oneliner extracting direct mp4 link from YouTubeCenter plugin = streaming video in mplayer without downloading.
A: "holy crap that is convuluted"
I do not use Python nor a Javascript-enabled web browser to download video.
Both are big, convoluted, slow(!) and unnecessary.
But I do agree with using mplayer for playback.
I simply use mplayer and javascript oneliner extracting direct mp4 link from YouTubeCenter plugin = streaming video in mplayer without downloading.