Working Youtube downloader extension for Safari?

Hi,

I've been looking tirelessly for a working plugin for Safari to easily download YouTube videos with a button/drop-down bar on the video page. However I've tried a few addons (keepvid, fastesttube to name a few) and none of them seem to do anything? Nothing appears on any youtube video and the addons were both fully enabled.

Does anyone know a working plugin for this? I'm on a brand new Macbook Pro with all the latest updates etc.