2016年6月17日
By 1月时特约编辑
专题文章

评论:V-Nova英仙座:它的压缩不辜负炒作?

V-Nova 推出压缩技术, 珀尔修斯, 2015年愚人节, 声称“平均压缩增益为2 - 3倍”, 在所有质量水平上, 在实际实时操作场景下与H.264, HEVC和JPEG2000.” The timing 和 the claims certainly raised some eyebrows among the compression cognoscenti, 把V-Nova当成了一个大目标.

大约12个月后，V-Nova兑现了其中一些要求. 但更重要的是, it has staked out a unique value proposition (UVP) validated with trophy client Sky Italia. That UVP enables IPTV distributors to deliver 珀尔修斯-encoded video at significantly reduced b和widths compared with H.无需更换编码设备或机顶盒.

正如今年4月宣布的那样, software updates enabled Sky Italia’s Harmonic ViBE VS7000 video encoders to output 珀尔修斯-encoded video 和 its set-top boxes to decode that video. Deploying 珀尔修斯 allowed Sky Italia to reduce its average HD bitrate from 8Mbps to 4Mbps, cutting b和width costs 和 allowing Sky to extend the reach of its service by distributing HD video to customers on slower connections.

在质量光谱的另一端，印度电影发行商 FastFilmz announced that it is using 珀尔修斯 to deliver ultra-low-b和width video to Android-based mobile devices in India. This agreement highlights 珀尔修斯’ low-bitrate quality 和 the ability to decode on low-end Android devices typical of the Indian market.

除了这些以分销为导向的交易之外，还有V-Nova的贡献产品, 哪些已经被多个供应商部署了好几年. Clearly, 珀尔修斯 is more than a bad April Fools’ joke, 和 it’s time to take a closer look. 在本文中, 我将描述这项技术是如何工作的, 讨论实现细节，如编码/解码和文件格式, 详细说明我的质量和解码复杂度测试的结果. 但有两点需要注意.

第一个, 完全披露:经过编辑的同意, V-Nova带我去米兰和意大利的Sky见面, 和 then to V-Nova’s offices in London to meet with the company’s staff 和 take a closer look at the technology, 支付所有费用.

第二个, 更重要的是, I wasn’t able to encode with 珀尔修斯 technology or decode on as many platforms as I would have liked to. V-Nova’s internal decoder is a complicated comm和-line implementation that the company was reluctant to share, 和 there were no commercial video-on-dem和 (VOD) encoders available for testing while I was writing this piece (though some should be available by the time you read this). 而不是, 对于这里的测试, V-Nova将三个标准测试文件编码为几种1920p配置, 我将这些编码与H进行了匹配.264和HEVC等价文件. 我可以在一台安卓平板电脑和一台 linux操作系统的NUC计算机这是我从伦敦带回来的，但不是在Windows或Mac电脑上. 所以让我们承认这只是初步观察, 和 I’ll be careful to detail as many assumptions 和 test details as possible so you can draw your own conclusions from the data.

对珀尔修斯

在高水平上, most video codecs encode frames by dividing the frame into blocks 和 squeezing data from these blocks as necessary to meet the target data rate. This causes the blocky artifacts we’ve all seen on streaming video 和 fringe cable 和 satellite channels. 珀尔修斯以多种分辨率处理每一帧, encoding the lower levels first 和 then adding detail as necessary for the higher resolutions. 我们将看到，这种模式避免了H固有的块性.264、MPEG-2和HEVC. 珀尔修斯倾向于在激进的编码配置下模糊.

珀尔修斯有两种口味:纯粹的和混合的. Pure 珀尔修斯在整个过程中只使用珀尔修斯算法, 它被用于V-Nova的贡献编码器中, 这个我就不讨论了. 混合的珀尔修斯, 这是为了分配, 结合了英仙座和其他压缩技术, 如H.264. 例如，混合动力珀尔修斯可以使用960x540 H.264-encoded stream as one of the lower levels 和 then build additional levels of detail to full 1920x1080 resolution using only the 珀尔修斯 codec. 这种技术有几个关键的好处.

第一个, 由于数据在文件中的打包方式(稍后会详细介绍), 像QuickTime这样的播放器可以播放低分辨率的H.264年文件. 图1 显示QuickTime播放器播放960x540 H.264年文件, which is actually a lower-resolution layer in a 1080p-encoded 珀尔修斯 file. This allows operators to distribute a single file with two decode resolutions depending upon the installed player.

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图1. QuickTime Player is playing the 960x540 file that serves as a lower level in a 1080p-encoded 珀尔修斯 file.

第二个好处是，如果H.264播放在播放平台上是gpu加速的, 珀尔修斯可以访问H的硬件加速.264层. 在我测试的安卓平板电脑上, this allowed 珀尔修斯-encoded files to decode at less than 50 percent of the CPU levels required for HEVC. 在本质上, this particular capability is what makes 珀尔修斯 decode possible on the inexpensive Android devices targeted by fastfilmz, 以及便宜的H.264台机顶盒. 这是HEVC根本无法比拟的功能.

注意H.264层 accounts for between 70 percent 和 80 percent of the total file bitrate of a hybrid 珀尔修斯-encoded file. 相应的, 如果使用更高质量的编解码器(如HEVC)作为基础层, 珀尔修斯文件的质量和/或效率也会提高. 虽然V-Nova已经在内部证明了这个概念, there are currently no commercial encoders capable of outputting hybrid 珀尔修斯 videos with HEVC as the base layer. According to the company, this is because V-Nova’s primary focus has been on the H.264改造市场，不与HEVC竞争. 一旦HEVC的部署变得更加普遍, the company will work with compatible encoder vendors to produce hybrid HEVC/珀尔修斯 files.

这种混合技术，显示在图2解释了为什么将珀尔修斯编码添加到现有编码器中如此简单. Basically, it’s a plug-in that sits on top of the encoder, receiving the lower resolution H.264编码视频并添加英仙座图层. V-Nova与Thomson进行了整合, 日本电报电话公司的数据, 和Imagine Communications, 以及其他几个编码器供应商. 在解码方面，这是相同的模式:本地玩家解码H.264 video 和 h和s it off to the 珀尔修斯 plug-in to process the additional layers. 除了VisualOn, 我测试的是谁的Android播放器, V-Nova曾与Wyplay合作, 是谁在意大利为天空电视台整合机顶盒. V-Nova offers encoder 和 decoder software development kits to enable this third-party development.

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图2. 珀尔修斯 OTT的实施只需要很少的资本支出.

完成图片, the 珀尔修斯-enabled encoder creates a st和ard MPEG-4 elementary stream with the 珀尔修斯 enhancement layer packed into the stream as supplementary enhancement 信息 (SEI), or it creates an MPEG-2 transport stream with the 珀尔修斯 layer included as a separate component. 无论哪种情况, 如果玩家知道如何处理这些数据, it decodes it; otherwise, 它忽略了它.

通过使用基于标准的格式以及编码器和解码器插件, 珀尔修斯实现起来相对简单. I spoke with Dominic Charles, joint-CEO 和 co-founder of fastfilmz, when I was in London. 负责编码和解码, 他打了两个电话——一个给日本电报电话公司的数据编码, 另一个是用于Android解码器的VisualOn. This freed him to focus on mission-critical tasks such as sourcing his content 和 planning marketing 和 distribution.

评估英仙座编解码器

Of course, just because a codec is easy to implement doesn’t mean you should use it. Let’s turn to the qualitative 和 performance evaluations, starting with quality.

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