i've extracted the Camera file from my G Flex which is already running the 4K on 4.2.2
i'm on international version of D958 10c Hongkong.
this is just to try if you guys are desperate for 4K video recording.
extract the 2 files and place them in system/app replacing the existing one's but before doing so please backup the original files at a safe destination so that if it does'nt work's, you can always restore your original files.
it's a very safe mode. replacing camera file's cannot brick any mobile. but still you as per XDA Rules you are doing this at your own risk if camera app disappears, install lenovo camera which gives even more freedom
first try by giving a normal permission like rw-r-r and if have issues try giving full permission.
Please report if it works
have a nice day!
PS : only for rooted stock odex stock rom