Google had tried and largely failed to get much traction in video on its own. As a remedy, it bought YouTube, a hot video startup, for $1.65 billion in 2006. Under Google, the service piled on new users and built up a gigantic library of clips. Revenues did take some time to figure out. But YouTube has since made huge progress, and according to one analyst, took in $2.4 billion last year after payments to partners were excluded.