What Does Netflix Know 关于 Prime Time Video Streaming, Anyway?

So, 我就在那里, making a presentation to a Scandinavian consulting client regarding the potential benefits of deploying HEVC or VP9 streams to compatible clients instead of H.264. It’s an issue I’ve gone round and round about in my mind because of one data point: Netflix’s ISP Speed Index, 美国的网速在4Mbps左右.S. 和许多欧洲国家.

根据Netflix, “The Netflix ISP Speed Index is a measure of prime time Netflix performance on particular ISPs (internet service providers) around the globe.换句话说, it’s about how much data Netflix can push through a particular ISP during prime time.

So, 我的想法是, 如果Netflix只能达到4Mbps的话, then that’s all this particular client would be able to push through. 就是这样，从H.264到VP9/HEVC不会降低带宽成本, it would simply substitute a 4Mbps VP9/HEVC stream for a 4Mbps H.264年流. The VP9/HEVC stream would likely have a higher resolution, 看起来会更好, 但这不会节省带宽.

I asked my audience, “What’s your average distribution throughput during prime time?其中一名成员说，“大约4Mbps。.我睿智地点点头, 后得出结论, “So, HEVC/ VP9将改善QoE, 但可能不会降低带宽成本.接着是一阵赞同的低语, and I was about to move on when another in the group raised his hand.

“I just finished a study of which streams are viewed by our VOD clients,” he began. “我们同时发行标清和高清视频, and 84 percent of all streams viewed by our clients are the top-quality HD stream, 8点mbps, 和最高质量的SD流, at 2.5 mbps. The reason our average throughput is 4Mbps isn’t because we’re limited by our ISP’s delivery capacity; it’s because we’re distributing a mix of SD and HD videos, 通常都是最优质的流. 我怀疑Netflix也是如此.”

哦. 你不讨厌这种事发生吗?

当然, these facts suggested a completely different conclusion regarding the economic benefits of deploying HEVC or VP9. Specifically, not only would it save bandwidth costs—likely cutting the 8Mbps HD stream down to 4.5 mbps or so and delivering lesser efficiencies down the encoding ladder—it would also boost QoE because lower-bitrate connections would be able to view higher-resolution, 高质量的流.

Later, the gent with the statistics was kind enough to share the stream distribution with me. While the HD/SD numbers were mixed, of the clearly HD numbers, 35.93 percent of the streams were the top-quality HD file 8点mbps, while only 2.6 percent of the streams were the second-tier HD file at 4.5 mbps. The vast majority of HD streams were delivered at the highest available rate. The bottom three video streams, all under 1Mbps, represented only .45%的视频流.

至少对这个制作人来说是这样, the Netflix ISP Speed Index had no relevance as a predictor of effective throughput. 有趣的是，在2017年 “互联网现状” 报告, Akamai 报告ed an average connection speed of more than 20Mbps in that particular country, which likely is the more relevant number to consider.

这是什么意思?? All encoding decisions must relate back to your own distribution patterns.

What’s interesting is how many important decisions this data can drive. 例如, my Scandinavian client was considering reducing the number of streams in the encoding ladder since several were retrieved by less than .百分之二的观众. 如果带宽受到高度限制, I’d recommend constant bitrate (CBR) or 110 percent constrained variable bitrate (VBR) for encoding to reduce stream variability and the potential for stream switching forced by data rate spikes in the stream, 而不是改变检索带宽. 如果不是, 150 percent–200 percent constrained VBR would deliver slightly better quality with little risk of deliverability issues. I might even consider capped constant rate factor (CRF) as a poor man’s per-title encoding schema.

The bottom line is, always make decisions according to your own log file.

[This article appears in the April/May 2018 issue of 流媒体杂志 “在黄金时段推送流媒体”."]