The Xperia Z2 is the sole handset from Sony that is capable of recording videos in 2160p resolution as well as in slow-motion mode. Thanks to some XDA developers now, owners of Xperia Z1 and Z1 Compact can also get these features on their devices.
Considering that both these devices are powered by a Snapdragon 800 processor, this should not come as a surprise since other similar devices like the LG G2 and G Flex also allow users to record videos in 4k/2160p resolution.
Installing the mod will require Z1/Z1 Compact owners to have an unlock bootloader as well as root access. Since this is the first release of the mod, it is slightly buggy for some users with some intermittent lag showing up in videos. Keep in mind that digital image stabilization is disabled while recording 4k videos, which will lead to a noticeable amount of jitter showing up in videos.
The Timeshift video feature is available as an add-on to the stock Sony camera app and will allow users to record videos in slow-motion. You can find the link to install the mod here.