OnePlus 5 Camera Mod (Requires Root) Enables HEVC/H.265 Recording
The HEVC/H.265 encoder is still in its infancy but a lot of people are already enjoying the benefit of its reduced file sizes. XDA pankajsammal, Member was able to modify the OnePlus 5 so that it can record videos in this format for 4K, 1080p, and 720p quality. This mod is also reducing the bitrate of of the recording to, so that will reduce the file size even more. To enable it, simply overwrite the /system/etc/media_profiles.xml file with the modded one provided in the thread (and be sure to backup your original).
Check out this camera mod in our OnePlus 5 forum