YouTube's video 'watch time' grew at its fastest pace in two years

Google unleashed a salvo of new YouTube video stats during its second quarter earnings call, as the Internet company looks to fight back against the rising threat from social network Facebook.

Google said that total YouTube "watch time" in the second quarter jumped 60 percent year-on-year, its fastest growth rate in two years. What's more, YouTube's watch time on mobile devices such as smartphones and tablets more than doubled year over year.

YouTube is increasingly prioritizing watch time over the sheer number of videos that are streamed, which is the preferred metric of Facebook.

Facebook's video streams have been growing like gangbusters, and are now up to 4 billion every day, thanks to its autoplay videos which automatically begin to play in users' news feed (Facebook counts any video that autoplays for three seconds or more as a "view").

Both companies are battling to make their online services the go-to destination for video viewing as smartphones and computers gain ground on televisions. At stake are billions of dollars in video advertising.

Google still does not break out the revenue and profit for its YouTube division. But Google executives reeled off a number of other interesting YouTube stats during the call.

YouTube reaches more 18 to 49 year olds in the U.S. than any cable network, said Google sales boss Omid Kordestani. And the number of users who start a video viewing session at YouTube's homepage is up more than 3x year over year, the company said.