The State of Codecs 2017
With the launch of HEVC Advance and formulation of the Alliance for Open Media, 2015年是近年来最具颠覆性的一年，因为它与视频编解码器的采用和部署有关. While 2016 was not quite so seismic, 在接下来的几年里，有许多重大事件将影响我们如何选择和使用视频编解码器, with one particularly unhappy holiday present for all H.264 users. I’ll discuss them here in mostly chronological order.
January 2016: U.S. HDR Market Converges on Two-Technology Approach
On Jan. 5, 杜比宣布，LG 2016年的OLED电视和超高清电视将采用杜比视界HDR技术, 这预示着杜比视界很可能成为美国事实上的高端HDR技术.S., with HDR10 as the royalty-free, but less featured, alternative. Admittedly, this date is arbitrary; we could have selected March, 当时杜比宣布亚马逊将在其流媒体4K游戏中支持杜比视界, or June, when Wal-Mart’s Vudu did the same. The key point is that support for Dolby Vision HDR is coalescing. Virtually all Dolby Vision-capable TVs will also support HDR10, which made it safe for TV manufacturers to build, and consumers to buy, 4K TVs with HDR.
This is significant, 因为在大多数正常的观看条件下，4k解决方案比1080p电视的优势微乎其微. 相比之下，HDR在几乎所有条件下都能显著改善观看体验. Unfortunately, 由于缺乏事实上的标准，内容开发人员的实际HDR部署已经放缓.
Dolby Vision has multiple advantages over HDR10, including 12-bit support as compared with 10-bit, 动态元数据可以逐场景甚至逐帧调整. 相比之下，HDR10使用在电影开始时发送的静态元数据. Dolby Vision can also support up to 10,000 nits of brightness as compared with 4,000 nits for HDR10, though it’s unclear when hardware that can display 10,000 nits will be available.
Fortunately, 内容制作人可以掌握杜比视界与后退支持HDR10甚至标准动态范围显示, simplifying production and distribution. Overall, 2017年应该是投资高端4K高清电视安全的一年, at least here in the U.S. In Europe, the BBC is pushing the Hybrid Log-Gamma (HLG) HDR technology, which it developed with Japanese broadcaster NHK. 到目前为止，虽然有一些投影仪支持HLG，但几乎没有电视支持. However, unlike Dolby Vision, which requires hardware support in the device, HLG should be field upgradeable via a firmware update. 因此，如果HLG在美国流行起来，许多HDR电视应该能够支持它.
Dolby Vision HDR appeared to become the de facto premium HDR standard.
March 2016: Beamr Acquires Vanguard
In March, Beamr是一家总部位于以色列的视频优化供应商，收购了编解码器供应商Vanguard video. This is significant for several reasons. From a technology perspective, 这一组合将使Beamr的优化技术能够用于先锋已经备受推崇的H.264 and H.265 codecs, rather than being applied as a post-process. This is more efficient from both quality and workflow perspectives, though Beamr hasn’t yet announced the availability of this solution.
From a pure heft perspective, the combination, which was enabled by a $15 million round of private funding, 使合并后的公司有能力与像Elemental Technologies和Harmonic这样的大型编码公司竞争. The merger is already bearing fruit; in December, Verizon Ventures, the venture capital arm of Verizon Communications, owner of Verizon Digital Media Services and other related companies, invested $4 million into Beamr. 这项投资可能预示着威瑞森数字媒体服务公司将使用Beamr的编解码器相关技术, and others in the family tree.
June 2016: Apple Supports Fragmented MP4 in HLS
At its 2016 Worldwide Developers Conference, 苹果宣布HTTP直播(HLS)将支持通用媒体应用格式(CMAF), a file packaging specification jointly authored by Apple and Microsoft. Why is this significant? Previously, HLS只支持打包在MPEG-2传输流容器中的文件, while the Dynamic Adaptive Streaming over HTTP standard (DASH), 以及专有技术，如微软的平滑流媒体和Adobe的HTTP动态流媒体(HDS), supported files packaged in the fragmented MP4 container (fMP4). 这意味着许多需要DASH和HLS支持其各种播放目标的发布者必须以两种格式生成和存储文件. CMAF enables a single format compatible with HLS and DASH.
美中不足的是，CMAF支持两种不兼容的通用加密模式:苹果FairPlay数字版权管理(DRM)技术的密码块链(CBC), and counter mode (CTR) for PlayReady, Widevine, and other DRMs. 使用CBC加密的内容不能被playready兼容的客户端解密, 而使用点击率加密的内容无法被FairPlay客户端解密.
Google has minimized the issue by supporting CBC in Widevine, which covers the Android platform, as well as Chrome and Firefox. Until Microsoft does the same for PlayReady and Edge, however, we’re stuck with two fragmented MP4 data silos, one encrypted in CBC, the other CTR. Or, more likely, until CMAF plays on all platforms, 大多数生产者可能会坚持使用封装在MPEG-2传输流包装器中的HLS内容, and DASH in fMP4.
August 2016: Apple Quietly Deprecates TN2224
Apple’s Tech Note TN2224 自2010年3月首次发布以来，它一直是编码专业人士的罗塞塔石碑, 提供关于如何制定编码阶梯的一般指导, as well as specific guidance on encoding for HTTP Live Streaming (HLS). On Aug. 2, Apple unceremoniously deprecated TN2224 with a short note stating, 重要:本文档关注的是实践及其背后的基本原理. 有关详细要求，请参阅Apple设备的HLS创作规范.” Well, at least Apple said it was important.
Interestingly, until Dec. 12, 苹果设备的HLS创作规范被命名为苹果电视的苹果规范. On that date, Apple amended the title to apply to all Apple Devices. 最终的结果是，您过去常常在TN2224中寻找HLS编码的具体指导, now you should look to the Apple Devices spec.
If you haven’t looked at TN2224 for a while, recent changes to it, and those engendered by the Apple Devices spec, have been dramatic. 苹果现在建议关键帧间隔为2秒(而不是3秒)，片段长度为6秒(而不是9秒)。. The encoding ladder itself has been completely revamped, and Apple now approves the use of up to 200 percent constrained VBR, perhaps the most significant change of all.
In addition, the Apple Spec recommends using the High profile, rather than the Baseline or Main, obsoleting several older iPhone models, 并且规定所有30i内容都应该去隔行化到60p而不是30p, a curious preference for smoothness over detail. Finally, 苹果设备规范指出编码阶梯中的2000 kbp变体应该是主播放列表文件中列出的第一个变体, making it the first retrieved by the player. The bottom line is that if you’re encoding HLS, you should check out the Apple Devices spec, particularly if streaming to an app that requires App Store approval.
2016年8月:Netflix大声宣称HEVC优于VP9，然后又悄然放弃
On Aug. 31, Netflix的Jan De Cock在SPIE数字图像处理应用会议上发表了一篇题为“Netflix内部大规模研究”的报告, “A Large-Scale Video Codec Comparison of x264, x265 and libvpx for Practical VOD Applications.“最重要的发现之一是，当用Netflix的VMAF基准来衡量时, 在所有测试分辨率下，x265的效率都比VP9 (libvpx)高20%左右.
Related Articles
4K is making inroads, 但是，高动态范围视频的深刻的视觉丰富性将真正改变人们看电视的方式. Streaming networks are leading the way.
30 Mar 2017
After a year of uncertainty, HEVC seems poised to finally make inroads, if not for 4K then for bandwidth reduction.
30 Mar 2016
H.264 still accounts for most video encoding today, but HEVC/H.265 and VP9 are beginning to make noise. What will 2015 bring?
19 Mar 2015
Companies and Suppliers Mentioned