An important development at WWDC 2017 in regards to video streaming was Apple’s announcement that it has officially chosen HEVC as its next-generation video codec. It will be supported on all iOS 11, tvOS 11, and macOS High Sierra devices. HEVC is also the foundation for 4K and HDR.
”In one word, efficiency”
Apple has been dancing around HEVC for some time but at WWDC 2017 the official word dropped. At WWDC’s ‘Advances in HTTP Live Streaming (HLS)’ session, it was announced that HEVC will be adopted widely across Apple’s products.
- “Apple has chosen HEVC as our next-generation video codec,” Roger Pantos, AVFoundation Engineer at Apple, announced. “Why did we do it? In one word, efficiency.”
HEVC (H.265) can reduce video bitrate “by up to 40% with same visual quality” compared to H.264 / AVC, according to Apple. Netflix goes even further by saying up to 50% improvement. As you may know, HEVC was designed first and foremost for 4K video but can also be used for HD video. The format is already being used to deliver 4K and HD video via streaming and on disc.
This is a very significant development. Google had been pushing Apple to adopt its free and open VP9 format but the company has ultimately decided to adopt the royalty-based HEVC. Even more significant was Apple’s announcement that HEVC will be supported on all iOS 11, tvOS 11 and macOS High Sierra based products.
iPhones and iPads based on the A9 chip or later as well as 6th- and 7th-gen Intel Core based Macs will support HEVC hardware acceleration after being updated to iOS 11 and macOS High Sierra, respectively. All other iOS devices and Macs compatible with iOS 11 and macOS High Sierra will support HEVC software decoding, which is notable for several reasons.
"And that will include the Apple TV with tvOS 11"
- “Even on older devices that don’t have hardware support we are still going to deploy a software HEVC codec,” said Roger Pantos. “That will be on all the iOS devices that will receive iOS11. And that will include the Apple TV with tvOS 11 and Macs which are upgraded to High Sierra.”
This small tidbit revealed during the session means that Apple TV4 will support HEVC software decoding once it is updated to tvOS 11. Apple TV4, launched in 2015, is based on the A8 processor.
A foundation for 4K streaming
HEVC was developed as a video compression codec for next-generation video, including 4K, 8K, HDR (High Dynamic Range), and HFR (High Frame Rate). HEVC is already employed on UHD Blu-ray discs and used by Netflix, Amazon, and others to stream movies and TV series in 4K and HDR quality.
HEVC is in other words a foundation for 4K video and HDR on Apple’s products. To be clear, HEVC will not make the Apple TV4 capable of delivering 4K video – HEVC can also be used for HD video – but it signals that the coming Apple TV5 will be capable of decoding 4K and HDR video.
Apple will include HEVC in HLS (HTTP Live Streaming) and employ it as fMP4 fragments. The company has decided not to support HEVC via MPEG2 TS, which is utilized in the UHD Blu-ray container and other companies’ implementations. Apple also introduced a new subtitle format, IMSC1, to HLS. It offers subtitles with “better control over styling” and is optimized for streaming. In addition, the new subtitle format will ensure perfect synchronization with video. At WWDC, it was also announced that HEIF (High Efficiency Image Format) will be adopted for image compression.
Apple adopting HEVC is important but not entirely surprising. HEVC will be the foundation under its video efforts in the coming years and signals that 4K, and possibly HDR, will play a much bigger role in Apple’s immediate future.