2019年6月3日
By 大卫·哈桑首席执行官,真实眼
专题文章

2019年流媒体播放测试工具买家指南

我在数字和流媒体行业工作了大约20年, 在过去的15年里担任RealEyes Media的首席执行官. 在那个时候, 我们公司已经承办了三届奥运会, 两次超级碗, 还有成千上万的现场活动, 除了开发流媒体应用程序.

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大多数时候我喜欢这份工作，但当事情进展不顺利时，我就讨厌它. 我的目标一直是找到最小化直播问题的方法. 为此目的, 我组装了一个视频工程工具箱，里面有诊断的解决方案, 修复, 分析, 以及解释流媒体视频的问题. 其中一些工具是由其他公司创建的, and others were developed by our team at RealEyes and are available to the industry to use.

我工具箱里的解决方案可以分为三类:

Network-type “over the wire” 太ls that analyze what’s being transferred to and fro in a live stream
工具 that go “under the covers” and attempt to identify what’s actually in the video that’s causing problems with the stream
解决我所说的“最后两英尺”的工具,“提供特定交付问题诊断的玩家.

了解更多关于“over the wire”和“under the cover”的解决方案, check out my Video Engineering Summit presentation from 流媒体 West 2018, 工具 & 诊断技术 & 解决大型活动中的问题.

这些“最后两英尺”的问题可能特别棘手, 这就是我们在这篇综述中要关注的. 我并不是每天都用这些方法, 但我都用过, and each one offers different features and benefits that I’ll discuss in this article. 对于每个工具, 我会告诉你要注意什么, 你为什么想要, 以及你需要怎样才能使用它. Some of these 太ls are pretty basic, but still useful in their own way; others get pretty deep.

VLC播放器

We’ll start with a player that should be familiar to just about anyone reading this article. 尽管在很多方面都有限制， VLC播放器 (图1) is a great player for getting started with testing, just to see how things work.

图1:VLC播放器

它不会给你很多的见解, but it’s a good baseline to make sure your video is playable in a general sense. The tricky thing with VLC播放器 is that I’ve seen it play a lot of things that other players can’t handle. 有点太在这方面很好.

Is it a great litmus to test to say, “OK, well, if it plays in VLC it should play anywhere”? No. 更有可能的是，情况正好相反. 如果它不在VLC播放器播放, 你可以相当肯定它不会在任何地方播放, 除非是由于身份验证, 令牌的问题, 诸如此类的东西. 但这就是为什么你提前使用网络工具.

Beamr视图

与VLC不同，波束视图(图2)是为比较质量分析而设计的. 这对于比较不同比特率之间的质量非常有用, 或者当你有两个不同的视频，其中一个有问题, 但它们应该是一样的. It’s also good when you’re just encoding video and you want to be able to visually validate stuff. Beamr视图 is not a conclusive 太l but instead provides an excellent way to make subjective visual decisions in a comparative A/B fashion, 它做得很好.

图2:波束视图

Beamr视图最棒的一点就是它是免费的. Beamr 不 make it sound like it’s free when you go to the site, but it actually is. 你只要跟他们说:“嘿，我想用这个，酷吗??他们会说:“当然，去吧。. 只要你没做不该做的事.” Beamr also has amazing encoding 太ls that may also be free, depending on your level of usage.

Beamr视图的比较分析主要是A/B，并且是逐帧的. 您可以在顶部获得数据指示，如图2所示. 在图2所示的剪辑中, 尽管这些都是独立的决议, 我让Beamr视图缩放到匹配，这样我就能看到. 它也有几种不同的方式，你可以看你的视频, such as moving the vertical line that splits the screen between the two different versions to see the quality benefit of one versus the other.

Beamr视图 also has a Butterfly View that flips one clip horizontally so you see the clips in a mirror image of each other. 还有双重视图和叠加. 您可以在所有这些视图之间切换. Split View (shown in 图2) is my favorite because it lets you do the back-and-forth.

Beamr视图 is also good for testing playback, plus handling emerging codecs such as HEVC. So when you’re wondering, “Am I really going to get a benefit from HEVC versus AV1 or H.264?“这是一个很好的开始评估的地方. (让我们明确一点:你应该得到好处.)

Telestream开关

One of my personal favorite “last 2 feet” 太ls—and the one I use probably the most—is Telestream开关 (图3). 它是一款付费游戏，并不便宜(售价499美元).包含诊断工具的专业版为99美元).

图3:电视流开关

之所以要花这么多钱，是因为Switch有能力解决问题, 尤其是字幕, 闭路数据, 诸如此类. Switch is one of the few 太ls that actually allows you to pull out your 608/708 data that’s in-band and fix the problems it diagnoses.

图3显示了Telestream开关 Pro中的播放器. All the little markers you see are actually showing your I-frames, P-frames, and B-frames. 黄线表示i帧, 紫色的线是p型框架, 蓝线是b帧.

为什么这很重要?? 如果我们的内容不是从关键帧开始，就会发生糟糕的事情. We always need that I-frame in the beginning, or a number of issues can arise as a result of that. One of the first things I always have to check is, what’s our keyframe interval? 关键帧的节奏是否恰当? 如果我们将关键帧设置为每2秒出现一次, we need to make sure that that happens and continues consistently throughout the video for each segment. 不这样做可能会在某些平台上导致问题, 尤其是当你开始在内容之间切换的时候, 比如广告. We have seen a lot more issues on OTT set-top devices struggling with improper or missing keyframes on segments, 在实时事件期间，哪一种情况会导致应用程序中途崩溃.

您可以在图3中看到其他关键帧. 通常，这些会在场景变化时发生. 当我们需要额外的关键帧时，这是很好的, but we need to always make sure to maintain our cadence with the set-interval keyframes. One weird thing that happens sometimes in Switch (for reasons I have yet to figure out) is that the player shows a blank keyframe in the beginning. 但如果我用其他工具播放视频, 例如FFprobe, 它不会显示这里有一个额外的关键帧.

除了额外的关键帧，我发现Switch是一个超级有价值的工具. 在过去，它帮助我发现了很多问题, 尤其是当我们尝试制作混合内容时, 或者测试潜在的编码问题. 如果一个流被切割和包装不当, Switch是一个很棒的视觉工具，它能让我真正看到这一点.

也, if we’re seeing bad things happening when we play back the video—bad blocking, 例如，能够在Switch中逐帧播放它真的很方便. 但它也有缺点，特别是在成本方面.

真实眼MOE:查看器

图4 展示了一个叫做MOE:Viewer的工具，这是我们在RealEyes制作的. MOE代表媒体编排引擎. 这是我们用于直播或视频点播和监控我们的客户流. One thing we’ve found with live events over the years is that we really need to pay attention to what’s happening in the manifest. 更新是否正常?? 我们有摊位吗? 舱单上的内容和内容有什么关系? Being able to test this stuff very quickly while carrying out all of the other tasks involved in a live stream just became 太 much to handle reliably.

图4:真实眼MOE:查看器

我们可以继续冰壶, 我们可以继续在浏览器中加载, but we wanted to have a 太l that provided these features and correlated to visuals. 所以我们创建了MOE:Viewer.

在MOE:Viewer中，我们曾经将其称为Manifest Viewer (图5)，您可以通过Manifest Viewer对话框中的下拉菜单保存会话. 如果放入一个流中，我希望能够不断地进行测试, 我可以将其保存为一个会话，然后随时返回. 图5中显示的是一个VOD文件. 如果要使用XMLHttpRequest (XHR)凭据, 你可以在里面设置一个全局令牌, 如果您有令牌访问.