什么是VP9?

这是我们的“是什么...?”文章, 旨在提供定义, 历史, context around significant terms 和 issues in the online video industry.

VP9是开源的编解码器 from 谷歌 that was developed from technology acquired from On2的技术 2010年2月估计售价124美元.600万年. The first 编解码器谷歌 released from this acquisition was VP8, which was paired with the Vorbis audio 编解码器 in the WebM file structure. VP9 is the next iteration of the 编解码器, which became available on June 17, 2013. VP9 will be the last VPx-based 编解码器 released by 谷歌, 由于该公司贡献了所有编解码器技术开放媒体联盟 2015年9月.

VP8和VP9都可以在免费的BSD下使用许可证 that enables users to deploy encode or decode capabilities in both proprietary software 和 open-source software without disclosing their source code in either instance.

VP9技术概述

VP9的开发开始于 2011年底. 编码工具包括多种预测块大小, from 64x64 down to 4x4; up to 10 intra predictors, sub-pixel interpolation; three different transform types; 和 entropy encoding. The 编解码器 supports a maximum resolution of 8192x4352 at up to 120 fps 和 multiple color spaces, 包括Rec 601, Rec 709, Rec 2020, smpte - 170, smpte - 240, 和sRGB. A technical paper detailing these 编解码器 components 和 operation is available 在这里.

VP9性能

In terms of performance, VP9 has been compared to HEVC 和 H.264 multiple times by multiple researchers with wildly varying results. 例如，在“HEVC /小时压缩效率的比较.265和VP9基于主观评价,作者:Martin Rerabek和Touradj Ebrahimi, 作者的结论是, "objective-based measurements shows that HEVC achieves average bitrate savings of 39.6% vs AVC和35.6% versus VP9, [while] subjective scores show an average bitrate reduction of HEVC by 52.与AVC和49%相比，是6%.比VP9低4%." In other words, HEVC was significantly better than VP9, which really was no better than H.264.

下一篇论文的题目是H的比较评价.265/MPEG-HEVC, VP9和H.264/MPEG-AVC编码器低延迟视频应用," authored by Dan Grois Detlev Marpea, Tung Nguyena, Ofer Hadarb. 在这里, 作者发现, 根据详细的实验结果, the coding efficiency of VP9 was shown to be inferior to H.265/MPEG-HEVC，平均比特率开销为32.5% at the same objective quality for the 1-pass encoding, 32.6%为2-pass编码. In other words, HEVC produced the same quality as VP9 at a data rate of about 32% lower.

其他测试结果更为阳性. Iain Richardson, founder of Vcodex 和 author of four video compression books, produced a 比较 in September 2014 largely based upon ratings by ten subjective non-expert viewers. He concluded, "At the higher end of the quality scale (i.e. lower compression), both HEVC 和 VP9 achieve a similar viewing quality to H.264，文件大小减少40-45%." In other words, HEVC 和 VP9 were at relative parity.

2015年4月，《百家乐软件app最新版下载》出版比较结果 showing that HEVC 和 VP9 produced virtually identical quality on the nine test samples. This was followed in November 2015 by the first HEVC 比较 released by the prestigious Moscow State University (MSU) Graphics 和 Media Lab. 在其研究, MSU found that HEVC produced the same quality as x264 at 82% of the data rate, VP9紧随其后，为87%, 领先于所有其他HEVC编解码器.

图1. Moscow University found VP9 very close behind the x265 HEVC 编解码器.

Most recently, on May 24, 2016, in an article entitled "Netflix讨论VP-9相关开发工作,——大卫·隆卡, Netflix的编码技术总监, disclosed the company’s preliminary findings regarding VP9 quality. Specifically, he stated "we are seeing very good results with VP9 vs. x264. Our current data suggests that VP9 is less efficient than HEVC, but still very good. We are currently conducting 编解码器比较s, will publish our results around the end of summer."

In 实际试验2015年4月，VP9和H.264 files downloaded from YouTube revealed that YouTube encoded VP9-based 1080p streams at a 43% lower data rate than H.264, with 720p streams about 35 percent lower, all with similar subjective quality. In encoding trials performed by JW Player prior to their release of VP9 in their online video platform, 该公司报告了超过H.264占整个编码阶梯的50%.

Encoding efficiencies have been criticized by multiple parties, 包括Netflix, 谁说, “VP9比x264慢得多...[和] we believe that the current libvpx VP9 encoder would benefit from some optimizations."在流媒体进行的测试中, while the 编解码器 proved very inefficient in a multiple-core environment, deploying multiple encoder instances on the same computer produced encoding 速度s only about ten percent slower than x264.

编码VP9

You can encode/decode VP9 in the comm和 line using executables (vpxenc.Exe)由谷歌. Alternatively, you can use FFmpeg if compiled with libvpx support as described 在这里. Using FFmpeg is simpler because the tool accepts many more input formats 和 provides much greater overall functionality.

Documentation for VP9 encoding with either executable is sparse. 您可以使用可变比特率进行编码, 恒定的质量, 约束的质量, 恒定比特率, 或者在无损模式下, 定义在这里. The most detailed explanation regarding VPX encoding is available on the VP8编码参数指南，它解决了编码质量与代码质量等问题. 速度, but most specific recommendations use VP8 in the comm和 line arguments, so the applicability of the documented techniques to VP9 are unclear.

The WebM Wiki supplies some VP9-specific recommended settings for VOD, 破折号, 恒定的质量, 约束质量在这里, 但在流媒体测试中, these settings proved very slow 和 the output quality was lower than presets supplied for our testing by JW Player. The JW Player-based presets used the capped CRF encoding mode, were substantially faster than 谷歌’s recommended settings as well as outputting superior quality.

如上所述, the other issue with VP9 encoding with either comm和 line tool is very low utilization of available CPU resources, particularly on computers with a very high number of cores. Developers seeking to build their own VP9 encoding systems will have to experiment to find the optimal settings, deploy multiple simultaneous encoding instances to achieve commercially acceptable performance 和 quality.

生产商s seeking to buy or 许可证 a third party encoder, 或者在云端编码, can find a 列表 of commercially available VP9 encoding tools/services 在这里, though the 列表 includes tools that support VP8 encoding 和 VP9 encoding, not just VP9. 已知的VP9支持者包括 JW Player在线视频平台(OVP), Zencoder, 亚马逊网络服务云编码平台; Wowza代码转换器, Telestream有利，不过这个名单应该会很快扩大.

Single file VP9-encoded files are typically distributed in the WebM format. YouTube distributes adaptive bitrate files encoded in VP9 using the 破折号 container (图2). To help promote consistent packaging of VPX-encoded files, Netflix has published a 规范草案标题VP编解码器ISO媒体文件格式, which details 破折号 packaging 和 common encrytpion via ISO/IEC 23001-7 Part 7.

图2. YouTube distributes VP9 encoded video in the 破折号 container format.

VP9播放支持

VP9 playback is available on the most current versions of browsers 铬, 边缘, 火狐, 歌剧. VP9播放在Android版本4中也可用.4+.

在硬件支持方面，Wikipedia维护了一个列表 of chips, CPUs, GPUs, SoCs that accelerate VP9 decoding available.

截至撰写本文之日, 该列表包括来自英特尔的多个cpu, 联发科MT6795, NVIDIA GeForce GTX 750 SE/950/960 (GM206 GPU), NVIDIA GeForce GTX 1070/1080 (GP104 GPU), NVIDIA Tegra X1, 高通骁龙820, 瑞RK3188, 三星Exynos 7 Octa 7420, 三星Exynos 8 Octa 8890.

谷歌 has made VP9 (和 HEVC) support m和atory for Android TV devices, VP9 playback is now starting to appear on many 4K Smart TVs like the 三星性能捆绑包48”. 许多权威人士和行业观察人士 have predicted that YouTube’s support for VP9 will compel most Smart TV manufacturers to support VP9 in 2016 和 beyond. 除了智能电视，还有 Roku 4媒体播放器还支持VP9(和HEVC)播放.

部署VP9

YouTube is by far the largest distributor of VP9-encoded videos, distributing 超过250亿小时到2015年4月，vp9编码的视频. 在与流媒体的对话, YouTube executives have stated that though the service currently streams 4K videos in both H.264和VP9格式，他们最终计划放弃H.并仅在VP9中分发UHD视频.

JW Player将是第一个部署VP9的OVP, 试验将于2016年4月开始, plans to start commercial streaming with VP9 before the end of summer of 2016. Brightcove has announced VP9 encoding support in their cloud encoding service Zencoder, 他们计划在2017年初在OVP中部署VP9.

知识产权问题

2013年3月，MPEG LA和谷歌签订协议 granting 谷歌 a 许可证 to technologies that "may" be essential to VP8 和 one "next-generation VPx" 编解码器, 结果是VP9. In return, MPEG LA dropped their plans to form a VP8 patent pool. 诺基亚是MPEG LA H的成员之一.264 patent pool, but didn’t sign the aforementioned agreement, later 起诉 Android许可方HTC, 声称VP8, 在Android操作系统中使用, infringed on one or more of its video compression-related patents.

当时, Florian Mueller, 权威的Foss专利博客的所有者, stated that the royalty picture for VP8 is far from clear. 穆勒在一封电子邮件中写道, "Claims that VP8 is now free from per-unit or per-implementer 许可证 fees are grossly exaggerated. T在这里 are simply too many video technology patents out t在这里, the backers of WebM/VP8 are primarily companies whose own patent portfolios are too weak to resolve patent infringement issues through royalty-free cross-licensing.诺基亚最终输掉了这场官司, 2016年4月, 穆勒评论道, "At this stage I'm not aware of any pending lawsuit over VP9."

开放媒体联盟

9月1日, 2015, 开放媒体联盟宣布成立, consolidating the efforts of open source 编解码器 developers 谷歌, Mozilla, 思科, 微软, 和英特尔编解码器, AV1, 这是预计发货到2017年3月底. As with VP8 和 VP9, the AV1 编解码器 will be completely royalty- 和 disclosure-free. AV1编解码器主要基于VP10, 谷歌 has stated that they will not deploy VP10 internally or release it publicly, making VP9 the last of the VPX-based 编解码器s to be released by 谷歌.