CDN77的Juraj Kacaba谈论低延迟流媒体和边缘
Juraj Kacaba，客户实施主管 CDN77，采访了创始执行董事蒂姆·西格林(蒂姆Siglin)， 帮助我流研究基金会, 特约编辑，流媒体, to discuss low-latency streaming and edge delivery in this interview from 流媒体 East 2023.
Siglin在讨论开始时提到他看到Kacaba给了一个 在内容交付峰会上的演讲 引起了他的注意. Kacaba谈到了在不破坏流稳定的情况下降低延迟的方法. “One of the problems we've had in the industry for a number of years is HTTP delivery is great from one standpoint, 但是当你做碎片化的MP4时, 你必须等待...共和党和诸如此类的事情，”西格林说. “我写了一些早期的论文 光滑的流，所以这一直是一个经典问题. And one of the issues that I've talked about years back was that we were painting ourselves into a corner where we had to wait for 30 seconds to do delivery. 所以你谈到了可能解决这个问题的方法.”
“通常, 在这些用例中，我们所做的是与客户合作，了解他们需要什么,Kacaba说. 从一开始, 我们就像, “好吧, 所以我们需要坚持使用HTTP，因为这是最常用的格式.“当我们想在社交媒体上使用这种解决方案时, 或者流行的流媒体应用, 我们需要一个在所有公共设施上都能得到支持的解决方案 iphone 还有其他设备. 我们选择HLS或MPEG-DASH的原因是什么. And then we ask, what's the normal way to lower latency, to manipulate the size of the chunk itself? 只有一个临界值——你可以切断它，然后它就会变得不稳定.”
“People have tried to take it below that threshold, it results in really bad video西格林说.
Kacaba说CDN77的方法是, “让我们生成数据块，并看看如何处理边缘的数据块. 所以，你学得越来越多. 假设你有5秒的时间. 因为它仍然是一个大块, 它是你在CDN上发布的一段静态内容，就像其他静态内容一样. 但是您可以做的是将数据块分割成更小的HTTP块, 然后把它推送到服务器, 甚至在客户端[请求]之前.”
西格林说:“所以你是在预填充。.
“是的，”Kacaba说. “我们已经把它推向了边缘. 而且，每个小的HTTP块都有关于下一个HTTP块的信息. 所以有一个恒定的HTTP推送来自原点. 我们这样做是为了确保无论何时玩家请求块, 我们至少已经缓存了一部分, 他们已经准备好交付了. 当然，你需要把所有这些都塞进四五秒钟, 取决于所需的延迟时间.”
“一些流媒体节目回来了， 我们请罗杰哑剧来谈谈他们的低延迟HLS西格林说. 你所描述的和那个有点相似, 或者基本上你可以使用标准HLS或标准DASH分割?”
Kacaba说, “我们想要关注的一件事是纯粹使用市场标准, 这是标准化的HLS, 或MPEG-DASH, 因为它是由CMAF包装的. So, 当你想在市场上部署这些解决方案时, 你需要确保玩家端和最终用户端的可用性, but you also need to ensure that it is standardized and it is easy to deploy for your clients, 这些应用程序的提供者是谁, 这就是我们要走的路.”
“So one of the issues of with looking low-latency HLS was you'd have to essentially convert 一切 转向低延迟HLS，”西格林说. “What I sort of hear you describing--and correct me if I'm wrong--is you could deliver it if you had a device that couldn't necessarily receive portions of the chunk, you might have to send it as the full chunk where the other ones who are more aware of that have the ability to repack it.”
“是的，就是这样，”Kacaba说. “这也是我们喜欢使用标准化格式的原因. 有一条很直的路. 即使设备不具备低延迟流媒体的能力, 您可以切换到正常的标准化和受支持的格式.”
现在来谈谈 (请求)合并 有一点，”西格林说. “I don't think a lot of people are familiar with that, that was something you alluded to.”
“所以，合并是一种一直存在的东西 清漆在相当长的一段时间里，美国的cdn一直处于劣势，”Kacaba说. “对我们来说，最主要也是最首要的问题是我们的工作 NGINX 请求合并. 在正常设置中，它本质上是不存在的. 所以这是我们需要克服的第一个大障碍, 我们需要从头开始编写代码. 我们设法做到了，所以现在我们甚至可以在NGINX上使用它. 这是我们迈出的第一步. What's the market standard, what is used, what we can utilize, how we can tweak it on our side? The reason we try to use all the market standards is so you can have your own encoders and your own stack, we can just fit our CDN into it and help you lower the latency on the network or on your side. And then we also can offer you our own built-in encoding and video processing solution to it. 所以我们的目标就是尽可能地开放实施. 您可以只实现CDN端来降低延迟, 但也要处理好你已经制作好的内容. 也, 如果你敞开心扉, you can use our own encoders and have more ways to tweak it and fine tune it to do a specific use case.”
“你主要关注的是直播吗??西格林问道.
“Well it's sort of half and half now because one of our main use cases is social media,Kacaba说. “我们现在在社交媒体上看到的是越来越多的直播内容. 越来越多的社交媒体应用将直播作为一个整体进行投资.”
“而且因为你在做社交媒体, 当然, 其中一个固有的问题是，你的产品主要面向移动设备西格林说. “与主动力装置相反. 有一件事一直让我很感兴趣，那就是我们试图降低HLS的延迟, 甚至关于DASH的讨论都是关于这些delta的, 你也在断断续续的网络上投递. 如果漏掉了中间的一个会怎样呢? 系统如何恢复? Does it have to wait for the full segment length of time to get the next set of packets?”
“我们对待它的方式是, 当你有请求合并时, 当然，这完全是多余的，我们希望能领先一步. 所以我们利用我们的私有主干把数据块放到它们需要的地方. 当然还有多层缓存, 因此，即使这些步骤中的任何一个连接断开并恢复, 它离下一步还很近. 这样你就有了一个更冗余的堆栈.”
“So essentially you've verified that it's made it out to the edges of your path before you then release西格林说.
“没错，”Kacaba说. ” HTTP推 you can actually verify you have the segments where they need to be before they're served to the customer.”
这会增加多少额外的时间?西格林问道. “因为很明显，TCP/IP的一个特点是, 握手确认是需要一段时间的.”
“当它在亚秒级的超低延迟空间内不移动时, a few milliseconds here and there is exactly the buffer that you need for these types of steps,Kacaba说.
“而且你待的时间比窗口问题还长?西格林问道.
“即使 WebRTC在美国，你仍然有这个小小的缓冲，但你总是需要一个缓冲，”Kacaba说.
“That's something we've learned over the decades, is play it from the buffer西格林说. “不要试图马上就把它放进去, 尤其是当他们互相反目时.”
Kacaba说, “And you mentioned mobile devices, which is I think is a really good point. 现在越来越多的人通过移动设备和移动网络消费内容, 所以抖动是个大问题. Then you start implementing different solutions into the real world and at some point you ask yourself a question like, “好吧, 那么延迟有多短才是真正的延迟呢?你会看到最终用户是如何使用这项服务的, moving in the space of four to six seconds is usually the ideal space for social media. Because one thing is that the content producer--which is some tupe of person on social media--he wants 当然 to talk in the chat, 但也, social media needs to moderate the chat to have some buffer and to make the content safe.”
“It's the classic US broadcast dump button where you make sure something [inappropriate] is not done [live]西格林说.
了解更多关于低延迟流和边缘 流媒体连接2023.
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