Android 4.4 has a new screen recording function for developers, but as the CyanogenMod team has already demonstrated, it can be adapted for more general use. Well-known developer Koushik "Koush" Dutta has taken advantage of this for Mirror, a new screencasting app for KitKat that allows any rooted user to either record video directly on a device, or stream to an Apple Airplay-compatible receiver like Apple TV. No custom ROM required.
Android has had native support for user-taken screenshots since 4.0, and a few OEMs like Samsung have had supported the feature even before that. But until now, getting a reliable video recording of your device's screen has been a major pain, usually requiring some kind of root solution that doesn't work for all hardware. In KitKat, Google is doing away with that, allowing end users to record video directly from the screens of their devices.