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Understanding the HEVC Codec: High-Efficiency Video Coding

Understanding the HEVC Codec: High-Efficiency Video Coding

Introduction to the HEVC Video Codec

What does it take to put a new video codec into production on approximately one billion devices? With the omnipresence of iOS and the HLS protocol, the HEVC / H.265 codec reached a tipping point with global consequences at the 2017 Apple Worldwide Developers Conference (WWDC), where the company declared the HEVC codec its “next generation video codec.”

HEVC vs. AVC: What Makes the HEVC Codec Better?

From Apple’s announcement: “In one word, efficiency. And primarily, encoding efficiency. HEVC is about 40% more efficient than AVC. It means that your user is going to see startup at a decent quality 40% faster, and when the player adapts its way all the way up they'll see content that looks 40% better. We are making HEVC widely available. On our newest devices we have support for HEVC built into the hardware. Even on older devices that don't have that hardware support, we are still going to deploy a software HEVC codec. So, HEVC is going to be a lot of different places.”

With Apple’s commitment to the HEVC codec, and the hardware in most mobile chipsets already supporting HEVC video encoding at the time of the announcement, video providers understood that the HEVC codec had become the new video compression standard for streaming video.

Ultimately, the answers to every company’s HEVC vs. AVC analysis can be summed up in two fundamental benefits the HEVC codec offers:

  • HEVC is roughly twice as efficient as AVC
  • HEVC enables 4K and High Dynamic Range

Using the HEVC codec, you get higher video quality at the same bandwidth as AVC, or you can deliver the same quality at half the bandwidth that you could using AVC.

HEVC vs. H.264 vs. MPEG-2: Comparing Three Codecs

Simply put, the HEVC codec provides the tools necessary to transmit the smallest amount of information necessary for a given level of video quality. Here’s a comparison of the MPEG-2, H.264, and HEVC codecs by component.

COMPONENT MPEG-2 H.264 HEVC/H.265
General Motion compensated predictive, residual, transformed, entropy coded Same basics as MPEG-2 Same basics as MPEG-2
Intra prediction DC Only Multi-direction, multi-pattern, 9 intra modes for 4x4, 9 for 8x8, 4 for 16x16 35 modes for intra prediction, 32x32, 16x16, 8x8 and 4x4 prediction size
Coded Image Types I, B, P I, B, P, SI, SP I, P, B
Transform 8x8 DCT 8x8 and 4x4 DCT-like Integer Transform 32x32, 16x16, 8x8 and 4x4 DCT-like Integer Transform
Motion Estimation Blocks 16x16 16x16, 16x8, 8x16, 8x8, 8x4, 4x8, 4x4 64x64 and hierarchical quad-tree partitioning down to 32x32, 16x16, 8x8. Each size can be partitioned up to 8 ways, and does not need to be a square.
Entropy Coding Multiple VLC tables Context adaptive binary arithmetic coding (CABAC) and context adaptive VLC tables (CAVLC) Context adaptive binary arithmetic coding (CABAC)
Frame Distance for Prediction 1 past and 1 future reference frame Up to 16 past and/or future reference frames, including long-term references Up to 15 past and/or future reference frames, including long-term references
Fractional Motion Estimation ½ pixel bilinear interpolation ½ pixel 6-tap filter, ¼ pixel linear interpolation ¼ pixel 8-tap filter
In-Loop Filter None Adaptive deblocking filter Adaptive deblocking filter and sample adaptive offset filter

Comparing MPEG-2 vs. H.264 vs. HEVC Codecs

How Does the HEVC Codec Impact Video Content Libraries?

With media and entertainment companies curating and building large content libraries at a quickening pace, the HEVC codec can yield big bitrate savings. Organizations face increasing strain on their storage infrastructure as they strive to keep pace with multiscreen consumer demand. With the HEVC codec halving file sizes, you save on storage costs instead of having to double storage capacity.

What Bitrate Benefits Does the HEVC Codec Offer?

There are several cases in which the improved quality-to-bitrate ratio of HEVC will impact the industry. As high-quality video distribution consumes enormous network capacity, the benefit of these efficiency gains include:

  • Deployment of more channels over satellite, cable, and IPTV networks
  • Lowered cost of managed and unmanaged video distribution
  • Increased reach for bandwidth-constrained mobile and IPTV operators
  • Improved Quality of Experience of OTT services to match traditional broadcast delivery

How Does the HEVC Codec Improve Mobile Streaming, Ultra HD 4K, and 8K?

In the mobile streaming market, the HEVC codec offers bitrate reduction of 30–50 percent to achieve comparable quality to H.264, which is realized in video delivery cost savings across networks.

Assuming a given device can decode HEVC, mobile operators don’t need to deliver as much data for a given quality level, making for lower costs and more reliable video playback.

HEVC also aligns with the push towards high-resolution Ultra HD 4K and 8K video in the mainstream market, as only HEVC and newer codecs are broadly supported by TVs for 4K.

The main takeaway to remember: In general, HEVC should deliver the same quality video as H.264 at roughly half the data rate, though this will vary by type of content.

For a 1080p stream, for example, a publisher might be able to cut the data rate from 8Mbps to 4Mbps with no loss in quality. This reduction in bitrate can have a significant impact on edge cache costs because the file size is now smaller when video is delivered to end consumers.

And in some scenarios, like delivery to a high-resolution tablet via 4G, this may allow the viewer to watch a 1080p stream, rather than a 720p stream, improving the overall quality of the viewing experience.

Can Pay TV & Cable Companies with Set-Top Box Infrastructures Use HEVC?

For pay TV and cable using traditional infrastructure, such as older set-top boxes that can’t be upgraded, implementing HEVC is a challenge. However, some of these companies bifurcate their content delivery, and for the OTT portions of their business, HEVC solutions are much easier to create and implement.

Can I Mix the H.264 and HEVC Codecs in a Multi-bitrate Stream?

The answer to this question largely depends on the ability of the viewing device to seamlessly switch from H.264 to H.265 in mid-stream. Most devices, in the early days of HEVC codec adoption, chose one or the other, and there was not much mixing of H.264 and H.265 in the same multi-bitrate streams. But because both H.264 and H.265 fit into the same transport mechanisms, any difficulties mixing the two codecs aren’t an issue.

When Did the HEVC Codec Become Standardized?

Like the H.264 standard, HEVC is the output of a joint effort between the ITU-T’s Video Coding Experts Group and the ISO/IEC Moving Picture Experts Group (MPEG), which established the first version of the HEVC codec standard in 2013.

The ITU-T facilitates the creation and adoption of telecommunications standards and the ISO/IEC manages standards for the electronics industries.

Designed to evolve video compression, we can sum up the benefits of the HEVC codec in four points:

  • Delivers an average bitrate reduction of 50% for a fixed video quality compared to H.264
  • Delivers higher quality video at the same bitrate
  • Defines a standard syntax to simplify implementation and maximize interoperability
  • Remains network friendly—i.e. wrapped in MPEG Transport Streams