2019年11月11日
By 蒂姆Siglin 特约编辑
专题文章

战地直播:2019年的军事视频

对于许多军事单位来说, the tools of the trade for communications aren't much different from the ones you'd buy at your average big-box electronics store or mobile phone kiosk. 事实上, 根据本期采访的重点是执法和军事使用流媒体, the benefits of the latest smartphone may be just as appealing to members of a special forces unit that needs to travel light 和 fast over a long distance—but still maintain consistent communications 和 even send video or audio streams or recording—as they are to, 说, 普通的美国青少年.

五年过去了 “战地录像” article, 哪一个概括了我们对当时军事流媒体现状的理解, we’re taking another look at the types of use cases in which the armed forces—和 the support teams around them—leverage streaming technologies to protect 和 defend national interests.

这是对那些愿意为本文进行非正式讨论的特工和供应商的认可, 用例已被一般化，因此不提供具体的操作细节. 同时, 虽然, the key takeaways are presented in a manner in which the streaming industry can take actionable steps to further the use of streaming in military applications while simultaneously benefiting enterprise 和 entertainment customers that need quality live streaming 和 subsequent content archiving.

There are several companies worth noting in this space that directly offer products 和 services to military providers, 都在美国.S. 在盟国也是如此. 其中包括Vitec，它有各种各样的产品，比如扑克牌大小的, 无风扇的, ruggedized encoders that rose to fame by being velcroed into Humvees to add an “extra set of eyes” for vehicle occupants as well as encrypted digital signage solutions— 和 Red5 Pro, whose peer-assisted WebRTC solutions provide ultra-low-latency streaming for drone 和 advanced analytics solutions.

最后, 在我们深入研究一些军事用例之前, 读者应该注意到，来自战场的视频通常是直播流的最后一步. 绝大多数直播和随后的内容存档都是由更广泛的智能使用的, 监测, 和侦察(ISR)分析师社区，因为决策是围绕三个C做出的:指挥, 控制, 和通信. 想想杰克·瑞安(Jack Ryan)连续几天坐在办公桌前, 仔细看录像, 然后跳上私人飞机去异国他乡执行一项令人毛骨悚然但相对较短的实地任务.

HEVC获得动力

一开始, let’s look at one of the major advancements that has shaped the use of live-streaming video in the military 和 ISR market vertical: advancements in video compression.

围绕HEVC/H的炒作.265一直以来都认为它可以提供同等质量的流——也就是同样的内容, 带宽, 和网络拓扑——数据速率只有传统AVC/H的一半.264年流. 然而,, the overall uptake in HEVC has been slower than earlier adoptions of new video codecs (including historical uptake rates for AVC, mpeg - 2, 和 even VP-9 codecs) partly because of the continued improvement in data networks 和 partly because of the widespread adoption of— 和 “it’s good enough” mentality around—AVC.

而基于ip的无线(OTA)广播的出现——多亏了电视3.0规范 we covered in an article earlier this year—should result in an uptick in deployments for mass consumer usage of HEVC, the biggest gains in HEVC adoption in recent years have come from its use in closed-loop environments that need to balance the quality 和 deliverability of higher-resolution data streams.

军事垂直市场几乎是HEVC采用的典型代表, 和, 事实上, 这是一个HEVC应用蓬勃发展的领域. 这是一个引人注目的因素, 从战场的角度来看, HEVC带来的好处是在较短的地理距离内获得更高质量的图像吗. The use of microwave 和 other line-of-sight technologies to move extremely low-latency video imagery across a few square miles of a conflict hot spot means that the video compression won’t face any barriers in terms of network hops adding latency. 然而,, 鉴于这些视距技术的固定带宽特性, 在做出实时命令和控制决策时，每一点都很重要.

One interviewee noted that HEVC allows those using military theater video streaming to not have to decide between getting content faster or getting it at a higher quality, 因为HEVC本质上提供了比AVC更直接的好处. 然而,, those same benefits come at a cost when transmitting HEVC live video streams over congested or intermittent networks. 与AVC相比，其固有的能力更容易从最小的数据包丢失中恢复, HEVC的一个缺点是，即使是最轻微的数据包丢失，它也要敏感得多.

一位受访者将HEVC的视觉效果问题描述为几乎具有滚雪球效应, HEVC使用了更多的矢量帧, 但i帧更少, 导致的级联结果可能持续GOP的长度或更长时间. 在战区的情况下, 图像清晰度的丧失——或者, 在极端, the almost complete loss of visual imagery across a multisecond GOP—could exacerbate a life-or-death situation.

可能直接谈判

上述问题的性质并不局限于军事应用. 事实上, 正如我们在深入研究广播工作流程时所看到的那样, the use of HEVC as a contribution source from remote locations 和 even second-tier global sports venues has further shaped the need for FEC 和 error concealment techniques when the contribution feed encounters IP network congestion issues.

对于大多数贡献提要, 数据管道有足够的额外开销，可以部署FEC解决方案, 在发生网络拥塞的情况下，发送冗余数据包作为一种安全网. 除了, a bi-directional link between the remote site 和 the broadcast headend or master 控制 location allows solutions like SRT or 紫溪 to communicate back to the encoder as a feedback loop regarding the network topology.

这将导致以下两种典型情况之一:1)在合理的时间范围内, 数据包可以重传，以填补丢失的数据包, or 2) the 信息 about latencies 和 packet loss can be used to reduce subsequent encoding 带宽和 quality, 至少在网络环境改善之前.

在军事应用中, 然而, there is often neither extra 带宽 nor a backchannel on which to negotiate retransmission of particular packets. 鉴于之前提到的HEVC问题, 然后, there’s a very real possibility that the live video stream in HEVC could actually look worse than an equivalent AVC live stream.

为了解决这个问题，正在部署各种错误隐藏方法. 其中一种解决方案是内容感知编码和上下文感知编码(CAE)解决方案的巧妙副产品, 哪一个分析帧中的每个像素来决定在哪里最好地部署编码器的计算预算. 随着HEVC的出现，平衡有限计算百家乐软件的需求只会增加, which typically requires double the computing power of AVC to effectively enhance the video quality while still maintaining 带宽 savings.

While most CAE solutions only look at a single frame (or perhaps a few frames before 和 after the current frame being encoded) to establish both a priority ranking of important pixels as well as an overall computational bit budget, 它们通常在对单个帧进行编码后转储这些信息. 这样做是有道理的, 在某种程度上, since single-frame encoding is often required to deliver extremely low-latency delays (less than three frames or 100 milliseconds) when transmitting live streams. 然而, 我一直觉得, 大约5年前，他在一家CAE解决方案公司工作, 像素优先级排序和位预算数据必须具有一些附加价值.

事实上，它们确实如此. One company showed me a solution in which it leverages that derived pixel-priority data at the viewing application level to act as a form of error concealment. 在所谓的观察者侧错误恢复和隐藏, the viewing application uses historic frame data to temporarily replace artifacts with objects from prior frames. 因为这发生在查看应用程序级别, 实际上，不需要重新发送额外的数据包, 根本不需要反向通道——解决方案, 因此, 不会给观看体验或编码过程增加任何延迟, 由于在错误隐藏中没有使用来自未来帧的前瞻性信息. 通过记忆历史帧中像素的值, 插值像素的值, 并在回放查看器中注入一个实际的像素, 总的好处是消除了前面提到的HEVC编码的滚雪球效应.

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