41 Percent of YouTube Viewing is on Mobiles

Some idea of the rapidly-growing traffic demand represented by video can be gleaned from one bit of news: 41 percent of YouTube traffic now occurs on mobile devices (phones and tablets), up from about six percent of total traffic in 2011.

To be sure, that traffic appears mostly to happen when mobile devices are connected to Wi-Fi networks. 

In part, increased mobile viewing of mobile video will help justify or spur adoption of mobile broadband. For the most part, mobile devices will be used to watch video while connected to Wi-Fi networks in peoples' homes. 

source: Mobidia

That does not yet appear to the case on every mobile network, in every country. 

Still, the dominant trend is for users to switch to use of Wi-Fi when they can, especially in the home, and especially when they will be watching video.