One of the best third party YouTube apps on Windows Phone, Tubecast, gets Full HD and 60 FPS video streaming support and QuadHD (4K) support.Version 2.9.8 of the app brings some significant viewing improvements, including some ultra-high resolution support.
- Cast QHD Full HD & 60fps to DLNA devices
- Preload QHD, Full HD & 60fps videos
- Channel Menu: New design (Windows 10 style) with smooth animation.
- Thomson TV & Android TV added to Tubecast list
- Bug fixes
Obviously, your phone should be strong enough to show these high definition videos seamlessly. The lower end Windows Phones struggle with ultra definition video streaming and you MAY notice some audio desync and lag in devices like the Lumia 520.
Get Tubecast at http://www.windowsphone.com/s?appid=bee1728a-4c19-495e-86b2-ce13e4eaa6d4