The Windows Phone 8.1 leaks are intensifying - we saw a ton of screenshots but seeing the OS on video is much more revealing. It's an early emulator build but it already shows some interesting things about Microsoft's new mobile OS.
First off, things that are missing – no notification center and no Cortana. These might not have been ready for this particular build (note that this is a leaked build, not an official release).
Anyway, changes in the UI are pretty extensive. First, the navigation buttons have moved on-screen. This allows customization – they can be hidden by apps (and revealed with a swipe), you can set their background to match that of the app or the highlight color. You can see those settings in action at the 3 minute mark.
Earlier on in the video, the app switching UI is demoed and it looks the same as before, but now you can swipe apps away instead of hitting the X button (this is at the 1 minute mark). Opening new apps shows a splash screen while the app loads, similar to desktop Windows 8.1 and iOS.
Another change relating to apps is that this build provides an option to store apps on a microSD card similar to Android (option at 9 minute mark). This could be huge for low-end devices with small storage.
Internet Explorer 11 brings a revamped UI and engine too – YouTube now works much better and tabs show up as individual entries in the app switcher interface. The browser also adds support for WebGL (web-based 3D graphics). The camera UI has been changed a bit and now features a Burst shot button. The volume controls have also been revamped and now you get more granular settings.
Here's the video demo in question: