Video: Key Considerations of Migrating to VP9 for Live Encoding

了解更多关于广告插入的现场活动流媒体的下一个事件. Watch the complete video of this presentation from Video Engineering Summit at 流媒体西部, VES105. 直播与VP9在Twitch电视, in the 流媒体会议视频门户.

在Twitch，我们决定从H.264到HEVC或VP9从三个角度:

legal risk
可用解码器支持
以及压缩效率和压缩增益.

HEVC的法律风险

对于HEVC来说，法律风险(Figure 1, below)可能是我不需要谈论太多的事情. 专利机制, 池的数量, and the amount of confusion it's bringing to the market is beyond OTT and thus for itself.

Figure 1. HEVC legal risks

As you can see there are already three pools and there are even people with patents which are not in any pool. Some of these pools have already defined cost for content (Figure 2, below). Specifically, MPEG-LA is free, HEVC Advanced only recently moved for content to be free, Velos Media还没有定义.

Figure 2. HEVC版税结构

Other patent holders need to be treated case by case, and that's really not a comfortable position. And, although, for content, 我们似乎正朝着免费内容的方向发展, 就人们观看我们的设备而言, 如果设备端不支持HEVC, 我们直播给他们看没有意义.

And to be honest, although it is very expensive, the highest risk is that it is unknown. So that's what gives lots of incentive to the industry not to deploy HEVC to a big extent nowadays.

VP9的法律风险

VP9并非没有风险. 尽管VP9说它是免版税的, there is always a possibility for anyone to come and challenge Google for that. 尽管谷歌正在大规模使用VP9, and there is talk that Google has already signed a deal with MPEG-LA to cover the two generations which are VP8 and VP9, 但还是有一点风险.

Decoder Support

至于解码器的支持, 我将其分为三个方面:浏览器支持, hardware support, 一般设备支持. As you can see in Figure 3 (below), the five left columns are for desktop and laptop browsers and the rest is mobile devices. 你可以看到最上面一行，H.264，几乎无处不在. That's the universal encoder so far and probably the last universal encoder.

Figure 3. 解码器支持:浏览器

Firefox或Chrome不支持HEVC, but VP9 is, and Chrome is probably the top browser used by most platforms. So there is a little advantage in terms of playability for VP9 with Chrome and Firefox. 对于移动设备，H.264无处不在(Figure 4, below). HEVC has been supported on iOS since 2017, and although it is required on Android devices starting 5.0 and beyond, lots of devices will still have hardware HEVC decoding. 这又回到了许可问题.

Figure 4. 解码器支持:移动

VP9, obviously, 在iOS上不支持, 也许永远都不会, but it is fairly mature and available on lots of devices. The graph in Figure 5 (below) shows that, in general, 如果你看一下桌面的安装基础, laptop, 移动平板电脑和联网电视, VP9的渗透率几乎是它的两倍.

Figure 5. 解码器支持:安装基础

这些数据来自2017年. 从那以后，我们看到双方都有轻微的增长, and we’ve also seen HEVC penetration start to go much deeper. But this still gives us a good base for VP9 to start with.

Viewership

推奇的立场是什么? 今天，我们只编码H.264. 如果我们开始添加HEVC和VP9， Figure 6 (below) shows the percentage of viewed minutes our viewers would watch using either of these standards. For HEVC on browsers, since we rely a lot on chrome or Firefox, it's only 2.8%, whereas 50% of our content could be delivered using VP9. For mobile devices, 7% of our content could be watched in HEVC. 主要是IOS设备. For VP9, with all the Android devices, it could reach 10%.

Figure 6. Twitch的收视率

That's another reason why we thought VP9 would be the way to go.

寻找软件编码器

Our next challenge was to find a good encoder that runs in real-time at 1080p60 which is our highest rendition. Before we did that, we did some software calculations and ran the experiments documented in Figure 7 (below). 第一列显示了我们的基准H.264 (x264)介质预置. We encoded whatever is available in HEVC software, just to have a rough guide, and we used x265.

Figure 7. 压缩增益:软件编码器实现

In order to achieve real-time encoding we needed to run ultra-fast, and in testing the performance was not much better than x264. VP9, the library available is libvpx VP9, which is the Google library. 知道我们已经实现了实时, 我们需要加快速度, 这比x264的结果更糟糕.

我们觉得VP9可以为我们带来一些东西, but we're stuck in the sense that there are no VP9 software encoders out there. 有很多人在研究HEVC编码. Lots of companies have built ASIC, FPGA solutions, and some software solutions as well. At the end of 2017, only four companies, as far as I know, were doing any work related to VP9.

与第三方供应商合作

So we needed to dig a little bit deeper, working with third parties. We started talking to NGCodec about their Video Encoder IP, and we realized that they were starting to develop a VP9 model for real-time implementation (Figure 6, below). We ran an evaluation of that towards end of 2017 and found that it does deliver, 几乎一致, 比H节省25%的压缩量.264.

Figure 8. 第三方提供的VP9压缩技术

该编码器将在VU9P FPGA上运行, 哪个是Xilinx FPGA, and Xilinx has been working with us to deliver the Scaler IP as well as helping us with the integration. 所有这些都将在AWS服务器上运行. 我相信你们很多人都熟悉F1的例子, which is an FPGA instance on the cloud that you can use. 这就是我们要部署这个解决方案的硬件.