What Are HEVC and AVC? H.265 and H.264 Video Codecs Explained

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Who doesn’t love 4K? With a whopping 8.3 million pixels, a 3840 x 2160 resolution is quite the luxury these days. With a 4K monitor or TV, movies and games look impeccably sharp and detailed, and productivity also gets a boost. But that’s assuming your content is actually being delivered in 4K resolution.

If you own a 4K game or a 4K Blu-Ray, for example, and you’re playing it on a 4K display, you’re in the clear. But when it comes to 4K streaming, there’s more involved. Part of that is due to video codecs, of which there are two key ones today: H.265 and H.264.

Long story short, both are international standards for video compression, so that things like streaming and storage are easier. H.265 is the successor to H.264 and particularly important for video in 4K and higher resolutions. And coming next is H.266.

What is a codec?

Before we get into the individual H.264 and H.265 codecs, you’ll first want to understand what a codec is. A codec can be software or a device that encodes / decodes digital signals. For example, if you use Windows 10, you probably have Windows Media Player, which has the MP3 codec (among others) and, therefore, can play many music files. However, Windows Media Player doesn’t have the proper codec for playing Blu-ray discs, so if you pop one into your PC, it won’t play on Windows Media Player.

Video codecs specifically compress raw video data into a smaller form that’s more appropriate for streaming, storage, broadcasting et cetera. A 4K video, for example, is comprised of a series of frames, with each frame consisting of 8.3 million pixels -- that’s a lot of data. A video codec, such as H.265 or H.264, makes running 4K video easier by taking away some of the footage’s detail. That process is called lossy compression, and you should note that too much lossy compression can lead to stuttering footage that doesn’t look smooth. After compression, your PC, TV or media player also uses a video codec to decompress this data for output.

H.265, also known as HEVC, is the most current video codec. It’s the successor to H.264, also known as AVC. H.264 was preceded by MPEG-4.

What is HEVC / H.265?

H.265 is the latest international standard for video compression (you can find the full specification here). It’s also known as HEVC, which stands for High Efficiency Video Coding. It dictates a standard approach to encoding and decoding video. H.265 also dictates the types of tools that the codec can use. Developed by ISO/IEC MPEG (Moving Picture Experts Group) and ITU-T VCEG (Video Coding Experts Group), the H.265 standard was first made available in 2013.

With H.265, you can stream in 4K, rather than relying on a physical storage source, such as a Blu-ray disc. Major streaming services including Netflix, Amazon and Hulu all use HEVC for at least some of their streams, even some that are 1080p. An H.265 video encoder compresses the source video (a series of frames), and that bitstream is then stored or transmitted. Then, a video decoder decompresses it to output a series of decoded frames.

One compression tactic H.265 uses is identifying macroblocks, which may all be the same color or same image (such as a background) for numerous frames, and storing/streaming them in blocks instead of storing / streaming the color of each individual pixel. This means the frame will ultimately be a smaller, more digestible size.

HEVC vs. AVC

Before HEVC / H.265, the standard was AVC / H.264. AVC is short for Advanced Video Coding, and the standard was first published in 2003.

HEVC compresses video in a more efficient manner than AVC but with the same level of image quality. H.264 isn’t efficient enough for 4K streaming, but with H.265 4K content is compressed to a size that allows for streaming over something like Netflix, assuming you have the recommended Internet speed. With H.265, the video data takes up less space or needs less transmission capacity than with H.264 but with the same level of quality.

One of the key ways H.265 is more efficient goes back to those macroblocks we mentioned. While H.264 can identify macroblocks up to 16 x 16 pixels in size, H.265 can work with macroblocks as large as 64 x 64 pixels.

Does my PC support HEVC / H.265?

In order for your Windows PC to play HEVC videos, you need to be running Windows 10. You also need an Intel 6th Generation Skylake or newer / AMD 6th generation Carizzo or newer CPU, OR an Nvidia GeForce GTX 950 / 950 graphics card or newer / AMD Radeon R9 Fury / Fury X / Nano or newer.

If you’re an Apple user, you need macOS High Sierra or newer.

Smartphones and other media playback devices can also playback HEVC video with the right hardware. Here are some SoCs known to support HEVC:

Qualcomm Snapdragon 805/615/410/208 or newer
Apple A8 or newer
Nvidia Tegra X1 and newer

Raspberry Pi fans will be happy to hear that the Raspberry Pi 4 B has HEVC decoding built into hardware, though earlier models do not.

H.266 / VVC: Coming Soon

This week saw the announcement of the H.266 codec, also known as VVC, which stands for Versatile Video Coding.

The H.266 codec is said to bring an improved compression algorithm. The result is the same image quality of HEVC but with with a 50% smaller bit-rate. This makes the codec fitting for high-res content, like 4K and 8K, and streaming through mobile networks used for smartphones. Generally speaking, reduced bandwidth is very promising for data caps and taking up less storage.

"Through a reduction of data requirements, H.266/VVC makes video transmission in mobile networks (where data capacity is limited) more efficient. For instance, the previous standard H.265 / HEVC requires ca. 10 gigabytes of data to transmit a 90 minute [4K] video," Fraunhofer Heinrich Hertz Institute (HHI), which announced the spec, explained.

"With this new technology, only 5 gigabytes of data are required to achieve the same quality. Because H.266 / VVC was developed with ultra-high-resolution video content in mind, the new standard is particularly beneficial when streaming 4K or 8K videos on a flat screen TV."

Additionally, H.266 / VCC will support 360-degree videos and HDR content.

But you'll have to wait a while before you can take advantage of VVC. According to Fraunhofer Heinrich Hertz Institute HHI, which developed the codec with the likes of Intel, Huawei, Microsoft, Qualcomm and more, the CPUs required to handle this codec aren't available yet -- -- particularly those for laptops.

HHI announced the first software for encoding and decoding that supports H.266 / VVC, in September.

This article is part of the Tom's Hardware Glossary