2014年11月26日
By 1月时特约编辑
专题文章

VP9的案例

Google’s VP9 plays on about 60% of browsers today, 而HEVC为0%, 它提供了与H相似的质量.264以50-60%的数据速率, and ultimately it may be the only UHD codec that plays on Firefox and Opera. And while VP9 may play only a minor role in broadcast markets, 移动, 或奥特, it may be an essential component for reaching the traditional desktop/notebook market.

让我们从质量说起. There have been three recent comparisons, including my own. 第一个是“Comparison of compression efficiency between HEVC/H.265 and VP9 based on subjective assessments,” by Martin Rerabek and Touradj Ebrahimi. 在这里, 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.

伊恩•理查森, founder of Vcodex and author of four video compression books, 产生了第二个比较. 尽管理查森的测试 were much less extensive, they did involve subjective ratings by ten subjective non-expert viewers. He concluded, “At the higher end of the quality scale (i.e. 低压缩)，都是HEVC

and VP9 achieve a similar viewing quality to H.264 with a 40-45% reduction in file size.换句话说，就是相对平价.

为了我的测试, which I’ll document in a future 流媒体 article, I asked Google to prepare their encodes for me, as did the supplier of an embedded HEVC solution. I also prepared another set of test clips using a highly respected enterprise encoder that used the x265 codec. I computed the VQM scores using the Moscow University 视频质量 Measurement Tool (which I 综述了的欧洲版流媒体 magazine) and verified the scores with my own subjective comparisons. My results more closely matched Richardson’s; in fact, VP9 produced slightly better quality than HEVC in eight of nine test cases.

I have more work to do on these comparisons, both to make sure I’m comparing apples to apples quality-wise and to assess encoding time and the required playback horsepower. 但我有理由相信, 在一天结束的时候, the quality produced by VP9 will be similar to that offered by HEVC.

更重要的是, as we transition away from Flash and towards HTML5, it’s likely that VP9 will be the only UHD codec that plays in Firefox and Opera. Today, Firefox, Opera, and Chrome—which together comprise about 60% of browser share according to w3counter.com—all play VP9, while no browsers play HEVC. Microsoft has announced HEVC playback support for Windows 10, which won’t ship until mid to late 2015. Though Apple and Google now offer HEVC on their latest 移动 OSs, there have been no announcements regarding Safari or Chrome, though I would expect both to support HEVC playback sometime in 2015.

然而, I think it’s very unlikely that Firefox, with 17% of overall browser market share, 会授权HEVC吗. 他们从未授权给H.264 (though some versions of Firefox could grab an H.264 decode from the operating system) or via Flash. With Microsoft only including HEVC decode in Windows 10, there will be hundreds of millions of computers without OS-based HEVC decode for many years to come. And while Adobe has announced that it will support HEVC playback in Primetime, it has not announced support for HEVC decode in Flash Player. So it’s likely that neither Firefox nor Opera will ever natively play HEVC—VP9 will be your only option.

There certainly will be some speed bumps on the transition from Flash to HTML5, particularly for those monetizing their videos and protecting them with DRM. 但转型将会发生, 从现在的情况来看, VP9 may play a much bigger role than HEVC in that transition, 而且快得多.

[This article appears in the January/February 2015 issue of 流媒体 magazine as "The 生产商's View: VP9的案例"]