What Is HEVC (H.265)?

这是我们的系列文章的另一部分 "What Is...?" articles, 旨在提供定义, history, and context around significant terms and issues in the online video industry.

HEVC (H.265行政摘要

H.265/High Efficiency Video Coding (HEVC) is the successor codec to H.264, which, like H.是由……联合开发的 ISO/IEC运动图像专家组和ITU-T视频编码专家组(VCEG). The primary goal of the new codec is 50 percent better compression efficiency than H.264 and support for resolutions up to 8192x4320.

HEVC技术背景

By way of background, the ITU-T began development of a successor to H.264 in 2004, while ISO/IEC began working in 2007. In January 2010, the groups collaborated on a joint Call for Proposals, 在MPEG会议上达到高潮 & VCEG Joint Collaborative Team on Video Coding (JCT-VC) in April 2010, at which the name High Efficiency Video Coding (HEVC) was adopted for the codec.

In October, 2010, the JCT-VC produced the first working draft specification, with the Draft Standard -- based upon the eight working draft specifications -- approved in July, 2012. On January 25, 2013, 国际电联宣布，HEVC已在ITU- t替代批准程序中获得第一阶段批准(同意), 同时，MPEG宣布HEVC在MPEG标准化进程中已被提升到国际标准最终草案(FDIS)状态.

In essence, 这意味着规范的初始版本被冻结，以便多个供应商可以最终确定他们的第一个HEVC产品. The current implementation includes a Main profile supporting 8-bit 4:2:0 video, 具有10位支持的主10配置文件, 以及用于静态数字图像的主静态图像配置文件，其使用与视频“内部”图像相同的编码工具.

HEVC将继续前进, with work already starting on extensions for 12-bit video and 4:2:2 and 4:4:4 chroma formats, as well as incorporating scalable video coding and 3D video into the spec.

How It HEVC (H.265) Works

Like H.264 and MPEG-2, HEVC使用三种框架类型, I-, 一组图片中的B帧和p帧, incorporating elements of both inter-frame and intraframe compression. HEVC incorporates numerous advances, including:

编码树块: Where H.264 used macroblocks with a maximum size of 16x16, HEVC使用编码树块, or CTBs, 最大尺寸为64x64像素. Larger block sizes are more efficient when encoding larger frame sizes, like 4K resolution. 如图1所示.

HEVC Figure 1

Figure 1. Larger blocks sizes enhance encoding efficiency. Images from HEVC webinar by 基本技术, 可以按需.

更多内部预测方向: Where H.264使用了9个帧内预测方向, HEVC可以使用超过35, 添加更多潜在的参考像素块，从而提高帧内压缩的效率(参见图2), from an Ateme演讲). The obvious cost is the additional encoding time required to search in the additional directions.

HEVC Figure 2

Figure 2. Searching is expanded to find more reference pixel blocks.

其他进步包括.

Adaptive Motion Vector Prediction, which allows the codec to find more inter-frame redundancies
优越的并行化工具, 包括波前并行处理, for more efficient encoding in a multi-core environment
熵编码只有CABAC，没有更多的CAVLC
改进了去块滤波器，并创建了第二个滤波器，称为样本自适应偏移，进一步限制了沿块边缘的工件

The HEVC (H.265)结果请

有许多已发表的白皮书和演示文稿集中于比较HEVC和HEVC的质量. H.264 and MPEG-2. One of the most oft-cited sources is an article entitled, 视频编码标准的编码效率比较——包括高效视频编码(HEVC), 哪个报告PSNR(峰值信噪比)比较和主观评价的结果. The report looked at multiple scenarios, including interactive and entertainment applications.

与娱乐相关的比较, the study encoded multiple clips ranging in resolution from 832x480 (480p) to 1920x1080 (1080p). For the PSNR-related tests, the study encoded files using four different technologies, HEVC, H.264, MPEG-4 and H.263，直到所有文件具有相同的PSNR值.

HEVC Table 1

Table 1. HEVC效率与H.264, H.263 and MPEG-4 using PSNR values in entertainment applications.

The study then showed viewers multiple files encoded at multiple data rates with H.264 and HEVC and asked them to grade the results. From these tests, 研究人员总结道, "the test sequences encoded with HEVC at an average of 53 percent lower bit rate than the H.264/MPEG-4 AVC HP encodings achieved approximately the same subjective quality."

另一篇文章 "Subjective Quality Evaluation of the Upcoming HEVC Video Compression Standard", compared H.264 and HEVC using both PSNR and subjective comparisons. 研究得出结论:

The test results clearly exhibited a substantial improvement in compression performance, 与AVC相比... For the natural contents considered in this study, 基于主观结果的比特率降低范围为51%至74%，而基于PSNR值的预测降低仅在28%至38%之间. 这种差异主要是由于PSNR没有考虑到人类视觉系统的饱和效应. PSNR也没有捕捉到工件的全部性质:AVC压缩序列表现出块性，而HEVC压缩倾向于平滑内容, 这就没那么烦人了. For the synthetic content considered in this study, 基于主观结果可以实现75%的比特率降低，而基于PSNR值的预测降低为68%.

It's reasonable to be at least a little skeptical of such results, since the comparisons were largely produced by technologists contributing to HEVC effort, 使用尚未发布销售或(在大多数情况下)甚至用于通用beta测试的编码器. 不愿透露姓名, 一家主要编码厂商的CTO估计，HEVC可以在1080p分辨率的相同质量水平下将文件大小减少30%, 在更高的分辨率下进一步增加.

HEVC (H)在哪里.265) Play?

回放统计数据更难获得. However, multiple companies have demonstrated HEVC playback on a tablet computer, including Qualcomm 在Android平板电脑上 1.5 GHz高通骁龙S4 dual-core CPU. Note, however, 视频的分辨率只有480p, which makes sense for tablet display but is far from the 4K video HEVC is designed to enable. 在2012年的PBS技术会议上爱立信表示估计编码HEVC可能需要高达10倍的计算复杂度，解码时的复杂度是2 -3倍.

根据一份题为消费类设备中的HEVC解码高级分析师米歇尔·亚伯拉罕来自多媒体研究小组据估计，在2011年和2012年出货的消费者设备中，能够通过软件升级进行HEVC播放的设备总数约为1台.4 billion, with over a billion more expected to be sold in 2013.

HEVC Figure 3

Figure 3. Unit shipment so HEVC-capable consumer devices (after software upgrades).

根据亚伯拉罕, in compiling these statistics she assumed that all PCs shipped in each year would be HEVC capable. The report also includes tables summarizing shipments of HEVC decode-capable tablets, 便携式媒体播放器, 流媒体播放器, 视频游戏机, Blu-ray players, digital TV sets, and set-top boxes.

Despite this significant installed base, analyst Frost & Sullivan believes that HEVC adaption is at least five years away for consumer content services. 延迟HEVC适应的因素包括最近许多付费电视运营商对AVC设备的重大投资, lack of broad-based support for HEVC in the OTT encoding and deployment ecosystem, and slow HEVC encode and decode chip deployment to preserve the profitability of existing AVC chipsets.

根据弗罗斯特 & 沙利文副总裁丹·雷伯恩, the initial HEVC rollouts will occur in closed-loop solutions like enterprise video conferencing, 远东地区的超高清服务, and low-bandwidth video-on-demand services worldwide, due to the potential cost savings associated with deploying lower bandwidth HEVC video. Rayburn预计卫星直接到户(DTH)服务提供商将在2014-2015年期间开始推出HEVC设备, with some pilot digital terrestrial television (DTT) channels expected in 2015. 然而，总的来说，他总结道:

虽然某些应用将比标准更快地接受HEVC, HEVC编码和解码核心将在2014年成熟, 我们预计将在2017年左右，第一代hevc产品的全面生态系统将进入市场. Furthermore, we expect AVC to remain in widespread use even in 2018, 尽管到那时它肯定会被认为是一种商品技术——就像今天的MPEG-2一样.

HEVC (H.版税将适用

One factor that may slow HEVC adaption is uncertainty surrounding royalties. Like H.264, many of the technologies contributing to HEVC are patented, and patent owners will want compensation for the use of their intellectual property. In June 2012, MPEG LA, a leading packager of patent pools, and the organizer of the H.264 patent pool, announced a call for patents essential to HEVC, and a third meeting of the 25 respondents occurred in February, 2013.

However, 据MPEG LA官方称, 对于版税指导方针的发布没有固定的时间表，甚至没有保证一个专利组织将会合并, 因为还有其他包装商, or the respective owners could decide to assert their rights individually. 一些细分市场, most notably chip, encoding, 以及其他基础设施供应商, 面对这种不确定性，他们是否会继续推进hevc相关的努力，而只是保留潜在的版税. However, other segments, 特别是免费流媒体内容的分销商，他们追求HEVC提供的带宽节省, will almost certainly wait until royalties are known.

HEVC即将迎来竞争.265)?

These royalties make competitive technologies like Google's VP9 worthy of mention, 尤其是自从谷歌加入 VP9解码到测试版的Chrome in December, 2012, along with a new decoder for audio streams encoded with the Opus codec. According to a 谷歌表示 made at the 互联网工程专责小组会议将于11月在亚特兰大举行, 2012, the goal of VP9 was similar quality as HEVC at lower data rates. In a requirements document available on the WebM website, 谷歌表示，除非VP9的质量比VP8提高50%，而解码复杂度只提高40%，否则VP9不会上市, 而HEVC是200%到300%.

As a codec, VP8 解析:选b.264, producing virtually the same quality at all tested data rates. However, 多重因素注定了VP8的失败, including the fact that Apple refused to enable VP8 playback on iOS devices or in Safari, that Microsoft 拒绝包含回放 Internet Explorer 9, that H.264 was a joint ITU/MPEG standard, and the fact that it came to market much later than H.264.

Many of these same factors are still in play: while Apple 有望接受HEVC, it's unlikely that it will support VP9 for the same reasons the company refused to support VP8; also, there are potential intellectual property issues. In addition, HEVC是一个联合标准, so it already has a vast head start in terms of silicon support for encoding and playback. Both VP9 and HEVC should appear on the market around the same time, however, 这可能会给VP9比VP8更大的机会.

Regarding the intellectual property issues: on February, 2011, MPEG LA发布了VP8专利申请2011年7月， 12个政党已经站出来. Still, there's no further progress reported on the MPEG LA website, and our MPEG LA contact confirmed that there was nothing new to report.

HEVC (H.265)

当然，就像《百家乐软件》里的雷伯恩 & 沙利文指出, HEVC can't be deployed until the full encode/decode/transport infrastructure is in place. 一些编码供应商，比如基本技术, 是否宣布所有现有的编码器都将在未来的某个时候通过软件升级来支持HEVC. Before purchasing an enterprise-class or even desktop encoder going forward, ask whether or not the encoder will support HEVC going forward, 以及这种支持需要多少钱.

Beyond this, precursors to significant availability of HEVC are market dependent. For example, in video conferencing, it's the availability of real-time HEVC encoders and decoders. 在流媒体领域, the playback side is always the driving force, 因为很少有制作人会将其编码为一种新的格式，直到它能够可靠地为一群有意义的观众播放.

For general-purpose streaming, it's hard to get excited about HEVC without:

来自MPEG LA的一套版税政策
在Flash player或Silverlight player等播放器中通过HEVC无处不在的播放(微软和Adobe都没有回应有关是否或何时可能发生这种情况的信息请求)
The incorporation of HEVC playback into the iOS or Android platforms, 要么通过应用程序，要么通过操作系统升级, 并明确指出哪些已安装的设备将在这些升级后支持hevc(考虑到两家公司的长期政策是不对未来技术发表评论), and the black ink-like opaqueness of their general-purpose dealings with the press, 我们甚至都没有问)
The availability of inexpensive decode silicon that can be incorporated into OTT set top boxes, 或者宣布一些现有的OTT机顶盒可以通过固件或软件升级来进行HEVC播放

Conclusion

Between NAB (April, 2013) and IBC (September, 2013) expect a flurry of announcements of HEVC-related technologies and products. During that time, the first wave of HEVC capable encoders and decoders will also come to market, making it possible to gauge the technology's real world performance, benefits, costs, and the interoperability of the encoded HEVC streams.

直到那时，就像冰霜一样 & 沙利文的报告显示, it's most meaningful to consider HEVC adaption in a micro rather than macro sense, since the precursors and economic drivers are different in each market. While the inevitable general-purpose buzz around HEVC is bound to reach Kaepernick-like proportions, what matters is how these announcements impact the markets that you serve.