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?
It is better to render your blender projects as images rather than videos because if you have render errors, it is easier to just re-render the failed image again instead of re-rendering the whole animation.
First of all, 4096x2160 is not UHD (4k) video resolution. The proper resolution for a 4k-UHD video would be 3840 × 2160.
I would try and render the animation as images with a resolution of 3840 × 2160. You could then use for example MakeAVI, to convert all your images to a video ( https://sourceforge.net/projects/makeavi/ ).