Why is HEVC better than H.264?

In macOS High Sierra and iOS 11, Apple will perform a new video encoding process technology, it is called “High-Efficiency Video Coding”, namely HEVC. It reduces video size and supports new high-resolution content while saving disk space. But what makes HEVC better than H.264?

Also known as H.265, HEVC is a video compression standard designed for the latest generation of high-resolution video. It is the successor to the widely used H.264 codec (also known as AVC or MPEG-4 Part 10), which has made some significant improvements to the current legacy compression scheme. In the end, HEVC (or H.265) may completely replace H.264, but this may take some time to actually implement.

HEVC was developed by the Joint Coordination Group for Video Coding (JCT-VC), which has been specializing in the development of video coding for compression standard technology since 2010. Apple announced support for the new standard at WWDC, which supports iPhone 6 and newer iPhones running iOS 11.

Why is HEVC better than H.264?

The HEVC codec offers more and better improvements than H.264. The H.264 codec was first developed in 2003 and has a long history. HEVC offers a lot of new features, but the advantages we mention next are what consumers care about.

1. Better compression

Compared to the H.264 codec, HEVC offers significant improvements in compression. In fact, HEVC compresses video twice as efficiently as H.264. With HEVC, video of the same visual quality takes up only half the space. Or, videos with the same file size and bit rate can exhibit better quality.

Part of this improvement is due to the increased macroblock size. Macroblocks are defined as image regions used for compression calculations, and larger macroblocks can effectively compress high-resolution video. H.264 only allows macroblocks of 16 × 16 pixels, which are too small to play videos above 1080p efficiently. HEVC provides 64 x 64 pixels macroblocks (now called coding tree units or CTUs) for higher coding efficiency at higher resolutions.

2. Improvement of interframe motion prediction

A major factor in video compression is the prediction of motion between frames (or lack thereof). When the pixel remains stationary (solid-state background image), the intelligent video codec can save space by referencing it instead of reproducing it. With improved motion prediction, HEVC can provide smaller file sizes and higher compression quality.

3. Improvement of interframe prediction

Video compression also benefits from the analysis of “moving” within a single frame, which allows for more efficient compression of a single frame of video. This can be done by using a mathematical function instead of the actual pixel value to describe the pixel layout. This feature takes up less space than pixel data, reducing file size. However, the codec must support sufficiently advanced mathematical functions to make the technology really work. HEVC’s interframe prediction function is more detailed than H.264, which supports motion prediction in 33 directions, while the latter supports only 9 directions.

4. Parallel processing

HEVC uses cells and fragment layers that can be decoded independently of the rest of the frame. This means that the decoding process can be split across multiple parallel processing threads and take advantage of more efficient decoding opportunities on existing standard multi-core processors. As video resolution increases, this efficiency requires decoding the video at a viewable speed on low-end hardware.

5. Higher maximum frame size

The world is becoming more and more “high definition” and HEVC supports this. With HEVC, video can be encoded up to 8K UHD or 8192 × 4320 pixels. Currently, only a few cameras can produce 8K video, and few monitors can display this resolution. But just as HD is today’s standard, we can expect 4K, even 8K, to achieve a similar

6. Hardware support

The HEVC codec is specifically supported by the current generation of Intel processors. The Kaby Lake family of processors includes a special instruction set for encoding and decoding HEVC video, so it’s almost certain that future Intel processors will do the same. This gives the HEVC codec an important speed and consistency advantage over other high-resolution video codecs. Given the popularity and technical advantages of the H.264 codec, Intel chose to have its hardware support HEVC, which is not surprising.