What is HEVC?
High Efficiency Video Coding (HEVC), also known as H.265, is a next-generation video compression standard developed by a group of encoding experts called the Joint Collaborative Team on Video Coding. The HEVC video format has been in existence since around 2013, and HEIF is the still-image version of the standard that both iOS 11 and macOS High Sierra also support. (You can learn more about HEIF here.)
Benefits of HEVC
Apple's decision to adopt HEVC basically means two things - higher quality video and better compression rates. The HEVC standard enables a video to be compressed into a file that is about half the size (or half the bit rate) of H.264 / AVC. To put that another way, a HEVC video file offers significantly better visual quality than an AVC file of equivalent size or bit rate. While results vary depending on the type of content and the encoder settings, videos encoded in HEVC typically exhibit fewer compression artifacts and offer smoother playback than videos encoded using AVC.
According to Apple, HEVC can compress 4K video files to up to 40 percent smaller file sizes than AVC without losing quality, which means users who upgrade their devices to iOS 11 and macOS High Sierra will be able to take the same high-quality videos without using up as much storage space. At the same time, transferring high-resolution video files between devices and over networks will require significantly less bandwidth, a key advance considering new 4K iTunes content launched for the new Apple TV 4K.
Compatibility and Support
To capture and encode video in the HEVC format, iOS devices need to have at least an A10 Fusion processor, so owners of iPhone 7 or later and 2017 iPad Pro are fully able to take advantage of the standard. To check if your device's camera is capturing video in HEVC, go to Settings -> Camera -> Formats, and ensure the "High Efficiency" option is selected.
All iOS devices running iOS 11 and all Macs on High Sierra will support HEVC playback, with encoding/decoding hardware acceleration on newer iOS devices and the latest 2017 Macs offering faster performance combined with less battery drain. Readers interested in further transcoding details are advised to watch Apple's dedicated HEVC codec video presentation.