低延迟视频流——你能做到多低?

Mention the word and you will strike fear into engineers and operations folks throughout the streaming industry. 设备听到它的名字就会颤抖. Let's talk latency—a topic where the debate and definition of deficiency is as old as the industry itself. 想想上周末你看的那场足球赛. 当帕特里克·马霍姆斯在25码处触地得分时你微笑着想着, “那家伙是怎么做到的?, 每一次?，你大概落后于游戏本身45秒. 当你走进客厅看到同样的游戏, 你挠了挠头，因为你的手机离你有多远.

In order to understand latency, we need to examine the components in a live streaming workflow. 一切都从实时信号开始, 它是否是一个完全生产的频道, 或者塔上摄像头的独特画面, 直升机, 甚至是一台相机. 然后信号被输入到一个通常称为编码器的硬件中, 信号在哪里被数字化. 从那里, the digitized version usually takes two paths—either into a cloud-based workflow where the contribution stream is then packaged into additional stream variations, or those same variations (called renditions) are created on the encoder itself for delivery. 这两种情况, the stream renditions are then either pushed or pulled to a content delivery network (CDN) where viewers are connecting to watch the 流 via a player on a range of devices. These various pieces and parts have generally delivered 流 that are roughly 30 to 60 seconds behind the live broadcast feed. By comparison, cable and satellite channels are delivered to the home 5 seconds behind the live feed. These values and the distance from the live signal to your ability to view the channel are referred to as latency.

虽然我不会进入流媒体格式的历史, 协议, 诸如此类, suffice it to say that with the advent of HTTP 在线直播 (HLS) in 2009 and its dependencies contributing to the great latency debate painted us all into a corner. 即使使用新格式，这也保证了一些延迟, given that the video segments introduced a storage challenge for legacy CDNs and an assembly challenge for players. 澄清一下, 这不再是一个问题, and CDNs like Fastly's were designed from the ground up to handle the smaller file fragments native to formats like HLS. This also helped alleviate some of the expense in developing and deploying Flash—at the time the dominant video format—and Steve Jobs had some very hot takes on the format itself. 下次再讨论.

那么什么是低延迟呢?

So, 正如我在上面概述的那样, 如果几秒的延迟是正常的, 说某事是什么意思 低延时? 在视频流的世界里, 从主观上看，低延迟意味着玻璃杯到玻璃杯的延迟为5秒或更少. 然而，一些组织和应用程序需要更快的交付速度. 结果是, some are using new labels like 'ultra-低延时' and 'near real-time' where video can, 在理论上, 发货时间小于1秒. 流应用程序的这一部分通常是为交互式用例保留的, 双向聊天, 以及实时设备控制(这在无人机的直播中很常见).

在播放器栏中向前滑动(看我怎么做的?)到2020年，我们正处于视频领域许多参与者实施的风口浪尖苹果新推出的低延迟HLS (LLHLS). 这对新闻发布者来说是个好消息, 体育和时间敏感的内容, 在这方面，规范提供了一个低至1到3秒延迟的路径. 供参考, your service provider (cable/satellite) generally delivers content to your television at 5 seconds behind the live broadcast. But LLHLS isn't mandatory to achieve a solid streaming experience for your customers or viewers. 对于大多数非时间敏感的场景，旧的HLS很适合你.

为什么低延迟很重要

如果新闻, 体育, 或者对时间敏感的应用程序是您业务的一部分, 今天，您绝对需要低延迟交付. 为什么? 简单地说，你的观众可以在2秒或更短的时间内看到直播内容.

以Videon最近与《百家乐软件app最新版下载》的合作为例. This workflow starts with the creation of the stream renditions on our Edgecaster device, eliminating the added latency that cloud processes like transcoding and packaging introduce. 虽然云转码方法没有任何问题, 这种权衡在增加的延迟和成本上得到了清晰的描述. The stream renditions are pulled from a high-performance web server that lives on the device and are delivered through the Fastly edge cloud. 最后一步是将工作流与启用了低延迟的播放器结合起来. 这种方法适用于许多玩家. 在这种情况下, Videon worked with NexPlayer technology and have seen great results across multiple platforms. 整个工作流程如下图所示.

使用此配置和工作流，我们共同观察到1.2- to 1.7秒范围. 这是跨工作流所有组件的出色性能. Fastly's director of product management Dima Kumets was impressed when he saw the real-time latency readings. fast的106Tbps全球网络(截至9月30日), 2020年)为世界上一些最大的流媒体服务提供视频. 我们在与Videon合作时看到的结果非常出色."

We partnered with Fastly because we knew its network could deliver exceptionally high performance in this scenario. 虽然此解决方案可以与大多数主要的cdn一起工作, 我们对Fastly提供的性能和整体体验非常满意. But one key takeaway is that more and more organizations are looking at this type of architecture for 低延时 delivery, 视频能在哪里生存, 接近源馈送和边缘网络. 这可能是未来几个月的关键生存策略.

一种新的视频处理方法

澄清一下, 我们在这里没有使用任何“特殊酱料”, 也不使用新的专有流程或插件. 作为老工业盐，我是, I've seen far too many very interesting approaches to new video processes that require the user and video processor to jump through far too many hoops to get to first frame. 在今天的超大规模视频世界中，视频每小时都呈指数级增长, 我们不断面临提高标准的挑战.

提高标准, 至少这次是这样, 这意味着要使用一种新的方法，这种方法可以延伸到芯片组. 高通骁龙是比较成熟的ARM处理芯片, 在智能手机领域也很有名, 而是一种全新的用来创造和操纵媒体的工具 & 流. The Snapdragon chip itself provides native audio/video functions that can be leveraged which results in far less power draw while exponentially raising the amount of video that can be processed. This means no dependency on relics of the past like graphics processing units (GPUs) and lots of cooling fans. 确定, 也有一些方法类似于Videon的Edgecaster，使用不同的芯片组, gpu和更多的“重铁”, but for its capabilities as a video distribution and compute platform at its price pint, Edgecaster和这种方法不仅对低延迟用例非常有效, 但也有很多人. This is something we consider an unfair advantage in the market - Videon's unique relationship with Qualcomm and our ability to develop powerful and advanced edge and media processing capabilities on a device that no one else in the world has been able to do.

地平线上

所以不管你怎么创造超低延迟这个词, 超低延迟, 冷聚变低延迟(我开玩笑, 当然), 我们已经确定了低延迟意味着什么以及如何做好它. 随着高通的骁龙在随后的芯片组中越来越强大, the ability to process more media at the edge and to simply do more will grow exponentially. 这意味着分辨率、规模、体积等的提高. Further, it also means bringing more processes ancillary to video processing down to the device. 这意味着元数据的提取和分组, image recognition and basic analysis and many more processes that today run in the cloud could run more cost effectively at the edge and on this device. 而我们只是触及了表面. 事实证明，你可以做得很低——非常低——与其他以媒体为中心的功能一起，很宽泛.

[编者注:这是来自 Videon. 流媒体接受供应商署名完全基于它们对我们读者的价值.]