2016年7月7日
By 伊恩·瓦伦丁视频产品业务总监
专题文章

为什么端到端QoS和QoE多屏监控是必要的

Broadcast TV has set a high bar for viewer expectations and delivering a great quality of experience. As the trend and demand for multiscreen viewing and TV Everywhere continues to grow so does the demand for a high quality experience regardless of the device being used. Behind that multiscreen experience lies some complex adaptive bit rate (ABR) technology and a new set of monitoring challenges.

To give content providers visibility into their content and let them rapidly identify and address issues that impact user experience requires a sophisticated set of monitoring and analysis tools. Those tools need to provide comprehensive insights into both the quality of experience (QoE) and quality of service (QoS) on the delivery network being employed. These systems need to check everything from validating the availability of the assets to determining the quality of those assets even if they are encrypted.

ABR provides a mechanism for real-time and continuous display of video no matter how much or how little bandwidth is available on the device being used. It does this by fragmenting or packaging the content into small 2- to 10-second segments with several profiles (the same content at different bit rates) and then delivering the correct sequence of fragments at a bit rate that suits the 可用带宽. This means that to deliver a constant stream of content that does not falter the quality of the video will vary according to bit rate and 可用带宽. 当然, 比特率越高，体验质量越好, 但最重要的是，只要有带宽可用，视频就会继续播放.

任何ABR系统都是通过主动测量延迟来工作的, 可用带宽, 以及播放设备缓冲区有多满. 如果已满，客户端设备将请求较低的比特率配置文件. 当缓冲区清空时，设备请求更高的比特率配置文件.

图1说明了这背后的关键原则. In this particular example the segments are occurring on 2 second boundaries and it shows the seamless transition of the content on a device as it moves between different profiles. The same thing could happen on a single device as it moves between different networks and the overall 可用带宽 varies, 比如在Wi-Fi网络和手机网络之间切换时.

请注意，切换边界是至关重要的, 通常称为编码器边界点(ebp), 完全对齐. If they are not there will be discontinuities in the displayed video when the device switches between profiles.

One of the biggest challenges of content streaming is that the networks and devices are far more varied and non-deterministic than those found in the more controlled environments of cable, 卫星, 陆地, 和IPTV. Different network conditions and device requirements make such a highly adaptable architecture necessary in order to maintain uninterrupted content delivery.

随着ABR逐渐成为主流，现在也被用于提供线性内容, 服务提供者不仅必须确保转码器创建适当的配置文件, 而且，视频可以从采集(例如)进行监控.g., 卫星, 纤维, 文件)一直到原始服务器和内容分发网络(CDN)服务器.

为什么显示器?

为服务提供商确保他们正在交付, 或者将要交付, 一个伟大的经验，他们的客户需要做一些必要的检查. 在进行流媒体处理之前交付的内容质量是否良好? 资产是否要流式传输，并且如果请求，它的所有配置文件是否都可以流式传输? 如果是这样的话, are the asset and its profiles structured correctly to ensure seamless and problem-free playback?

回答这些问题需要一套工具来协助质量控制, 监控和测试资产的每一步. These range from real-time monitors capable of scaling to look at multiple programs simultaneously, 基于文件的QC工具来查看存储的内容, and monitors that can actively subscribe to an ABR service to ensure availability and quality of the content.

看什么和在哪里

任何ABR系统的核心都是包装器. 包装器执行三个主要功能. It transcodes the input content into multiple bitrates (on many systems there can be eight different bitrate profiles produced). 然后，打包器将这些配置文件分割成2到10秒的片段, 最后(在许多), but not all cases) it will encrypt the fragmented profiles before delivery to the origin servers or CDN.

Streams or content that arrives at the input to the packager have been initially monitored through the distribution network to the ingest point. This could be live content being received or episodic content being played from servers elsewhere in the network. It is important that the ingested content is error-free when received by the service provider. 如果摄取的视频和音频有缺陷, 这是不可避免的，最后的服务将是不可接受的.

There is a lot of content to be monitored at this point and any deployed solution needs to be able to scale to handle the volume and actually look at the content for QoE issues such as macroblocking, 压缩文物, 音频的沉默, 音频水平, 和响度. Similar tests may also need to be performed on episodic content using file-based QC tools on servers where the content is stored.

一旦内容被打包并交付到CDN, the only way to ensure that the content or assets will be available on request is to use probes or devices that can actively subscribe to the service. By doing this the probe can check the manifest for the asset and ensure that the various profiles are available for playout along with performing tests to check segment load and latency times. 除此之外, 探头可以检查ebp是否对齐，以确保在剖面之间无缝切换. The amount of content subscribed to by probes can be easily managed to minimize the load on origin servers or the CDN.

In situations where the content has been encrypted, basic probes can only provide QoS measurements. 有更先进的探测器可用, 在服务提供商的合作下, 允许对内容进行解密并执行QoE测量. 这让服务提供者知道，不仅内容可用于交付, 而且交货时质量也会很好. 需要解密的QoE测量往往更容易在托管网络中处理. 在非管理网络中, 探针需要与DRM供应商连接以获得对内容的访问.

Summary

有ABR流媒体服务, 结合使用来自摄取的QoS和QoE监控非常重要, 通过自动译码系统, 碎片, 并对所有可用的配置文件进行加密. It is critical to establish and test the content at the beginning of the chain to ensure what is going into the system is a known good entity. 在交货方面, providers need to test that the content will be available when requested and that it will play successfully. 简而言之, it is about ensuring that what goes in is great and what comes out leads to the best possible experience for the customer.

伊恩·瓦伦丁(伊恩·瓦伦丁)是视频产品业务总监美国泰克. StreamingMedia.com accepts vendor-contributed 文章 like this one based solely on their value to our readers.]