It's an understatement to say 4K content and products are on fire at the moment, with every manufacturer hopping on the bandwagon and getting 4K products out the door, stat. CyberLink is the latest to do that, with its mobile video editing app, PowerDirector, gaining the ability to edit in 4K.
CyberLink says this is the first time an Android app has been able to edit and output 4K content. Naturally, I tried this out on my Nexus 6P, and despite the fact a warning appeared when I added my UHD 4K footage, I didn't see any performance slowdown at all. To put it bluntly, all worked as expected, although it's true I wasn't editing the most complex of footage (less than ten seconds long, no less). I added a title, fade in and fade out, and some visual effects - the app managed all this perfectly. I attempted to export it in 4K, but found out I needed to pay for that, unfortunately.
Left: the warning that shows when adding 4K content. Middle: editing 4K video. Right: gah.
Apart from the aforementioned in-app purchase for 4K exporting, second video overlay, and the removal of in-video watermarks and ads in the app, PowerDirector is free to download on the Play Store. Alternatively, we have the APK available at APK Mirror, if that's how you roll.