The digital satellite TV service has launched Sky Go Extra, which lets Sky customers in the U.K. and Ireland download movies and TV shows over WiFi for offline viewing on mobile devices and laptops. Sky Go Extra is £5 per month for existing Sky customers and builds on Sky Go, the company’s on-demand service for mobile and connected devices (which is free to subscribers). Customers who sign up for Sky Go Extra can also watch on-demand streaming video on four devices, up from the two allowed under Sky Go.