Sample code that capture and encode video into HEVC (or H.264) with AVFoundation and VideoToolbox. The code is in Swift 4 and tested on XCode 9.2 / iOS 11.2.1 / iPhone X.

Based on tomisacat's VideoToolboxCompression project.

Brief instructions:

1. Build and run on iPhone 7/7 Plus or up. Touch Click Me to begin recording. Touch again to finish.
2. Download the result to Mac: XCode -> Window -> Devices and Simulators -> Select app and click the "gear" icon below -> Download Container.
3. Among the container files, tmp/temp.h265 is the raw HEVC data file.
4. Add a container around the file: mp4box -add temp.h265 temp.h265.mp4
5. Use QuickTime or VLC to play the mp4 file.
6. For comparison, you could change H265 to false in ViewController.swift to do H.264 instead of HEVC encoding.