Video is rendered at half the resolution I want to create a 4k video of a 3d animation so I've set the resolution to 4096x2160, the file format to QuickTime and the video codec to H.264 but I always get a 2048x1080 video. Which are the right settings to get a full 4k video?
Blenders default configuration sets the default resolution to 50%. Which means that it will render at half the size.

You can adjust these values in the properties panel under the 'scene tab'

For a full scale render set the resolution value to 100%