Live的到来.0

一个常见的问题是:“为什么直播视频如此复杂?, 为什么它与随处可见的视频点播(VOD)内容——包括YouTube上每天成千上万的新视频点播片段——有什么不同呢?

Simply put: The implications of on-time delivery of live events are significant. 发布VOD内容不受时间限制. 如果我们发布视频点播内容晚了几分钟甚至几天, 通常不会对商业或观众产生影响. 但是对于现场活动, 时机至关重要，因为有特定的商业影响，而且观众正在等待收看一场比赛，希望看到超级碗(Super Bowl)或NBA总决赛(NBA finals)的获胜者等对时间敏感的结果. 如果这些现场活动没有按时开始, 正如向数百万粉丝宣传的那样, 内容提供商将失去大部分观众, 如果不是所有的观众, compromising the content holder’s or distributer’s ability to monetize the event via pay per view, 赞助, 或广告. 内容在特定时间的可用性是关键的区别，也是创建实时内容并使其在线可用的关键风险. 这个关键元素对于将实时内容在线呈现给连接的观众所需的流程或工作流程具有巨大的影响.

视频点播和. 实时视频工作流程

简化后的形式, creating VOD content for online distribution involves transforming some form of mezzanine asset, 或高质量的源文件, 转换成一个或多个可供网络使用的格式, 这个过程称为转码. 有许多不同的软件工具, 或转换器已经, 哪个可以执行转码过程. 一旦转码成一个或多个网络准备格式, VOD内容放在原点上, 或内容起源点, and streamed to the viewer via a content delivery network (CDN). 如果由于任何原因，转码过程失败, one can simply restart it again; although it will take longer to make content available online, 内容的任何部分都不会丢失. VOD内容的质量取决于原始内容来源的质量和使用正确的转码配置文件(例如.g., 比特率的选择, 决议, and other transcode settings applied to achieve the best experience for targeted devices).

为在线分发创建实时事件内容, 也是它的简化形式, starts with content acquisition (typically through satellite downlink and decode, 视频光纤解码, 或IP组播), and encoding this live source 转换成一个或多个可供网络使用的格式. 然后将编码的内容实时发布到一个或多个发布位置，以便可以将其流式传输到ip连接的设备. 从表面上看，这个过程似乎很简单, but when you factor in availability of live content at a specified start time, 它很快从一个简单的线性过程转变为一个复杂的并行和时间敏感的过程，没有任何错误的余地. 复杂性很快由以下几个因素引起:

Inability to acquire live source, such as inaccessibility due to location
Changes in live source, such as receiving a live source at 480p when it was expected to be 1080i
Transmission issues, such as loss of signal or degradation in signal quality
Various encoding issues, such as dropped frames or out-of-sync audio
Publishing issues, such as inability to publish or interruptions in publishing

创建VOD内容时, we can simply readjust the process and restart it without affecting the video experience, 但在实时事件场景中，任何错误或中断都会立即以糟糕的用户体验的形式表现出来. 糟糕的用户体验可能是任何事情，从在指定时间无法使用的实时事件到根本无法使用. It can also include frequent buffering, freezing, out-of-sync audio, or macro blocking. 实时视频工作流中的任何这些并行步骤(单独或组合)都可以随时影响实时事件视频.

How do we improve this process to ensure a consistently great live video viewing experience? What are the improvements we’re going to see over the next few years in the live video workflow? Before we look forward, let’s take a look at what we’ve already seen.

生活1.0

In the early days of live video streaming dominated by RealNetworks RealVideo, Microsoft Windows Media, 和Adobe Flash, 数字媒体行业和观众对用于制作直播视频的软件和服务变得相当满意, as well as the quality of the video being played back mostly on PCs and Macs. To improve the video quality meant increasing video resolution and bitrate, and such increases closely followed adoption of broadband and increases in broadband connection speeds. 大多数时候, 观众可以选择比特率, 通常是3比特率——有时被认为是低的, 中期, 观众的期望值一般都很低. 除了一些零星的体育赛事直播, 媒体, 娱乐活动, streaming live mainly meant streaming corporate events and niche content. But the video experience was often degraded by buffering, dropped frames, and out of sync audio. 而在线直播体验是全新的，令人兴奋的, 视频观看的质量明显低于观众习惯的传统广播质量.

住2.0

住2.0 was ushered in with the advent of adaptive bitrate (ABR) streaming, 其中大部分是由Move Networks推动的. 自适应流使用自适应比特率(ABR), 客户端智能，不断测量客户端的互联网连接质量和CPU可用性，自动调整视频质量. All of a sudden, the possibilities were limitless for audiences and content providers. Users were no longer presented with confusing bitrate selections. 缓冲, 哪个是低带宽连接的常见问题, 显著减少，从而在广泛的ip连接设备上传输高质量视频. 随着这些技术和带宽速度的改进, 世界在网络上看到了第一个真正的720p高清视频. 包括迪士尼在内的各大媒体品牌, 美国广播公司, 狐狸, ESPN, 其他公司也很快注意到了这项技术，并首次提供了一些顶级优质内容.

除了ABR, adaptive streaming in its various flavors including Apple’s HTTP 在线直播 (also known as HLS), 微软的IIS平滑流, Adobe的HTTP动态流媒体(也被称为HDS)进一步提高了将优质内容无缝流传输到网络和移动设备的能力. Now instead of viewing on just PCs or Macs there were new devices streaming live video including tablets, 各种OTT设备，如Roku, Boxee, 苹果电视, 谷歌电视, 还有游戏机.

然而，这些技术的发展是有代价的. Adaptive streaming introduced additional complexities in terms of how content is encoded, 发表, 和保护, as well as how the overall workflow is managed and monitored. This in turn made monitoring and scaling much more difficult, and costs associated with this process went up significantly, creating barriers for entry and making ROI difficult to achieve.

Live的到来.0

所有这些都把我们带到了我们目前正在进入的阶段:直播视频发展的第三阶段, 或Live 3.0. 生活1的飞跃.0 to 2.0 was brought about by adaptive streaming, with a focus on improving the end viewing experience. 住2的飞跃.0 to 3.0是由实时视频工作流程的进步引发的, 从昂贵的硬件和基于SDI(串行数字接口)的基础设施转移到端到端支持ip的进程. The focus is now on improving the process in four key areas:

Solving for the complexity of multiple screen, formats, and platforms
极大地降低了将大量直播视频带给联网观众的成本，并改变了如何将获取的视频(从正在创建的直播事件中获取的视频)路由或发送到编码器或视频工作流管道的方式，在那里它将被处理为网络发布
具有弹性的可伸缩性，以提供扩展的灵活性，以数字化大量的实时视频, 当不需要这些百家乐软件时，也要缩减规模
实现对整个视频工作流管道的实时监控，并做出自动化的实时智能决策, instead of having to separately access various disparate parts of the video workflow pipeline, 推断和分析数据, 然后做决定.

如何实现这一目标? Advances in decoders and satellite receivers have led to the ability to output video in IP format, 打开了IP获取和路由的大门. 本质上, 不再需要将接收器连接到路由器到编码器所需的繁重的SDI布线和路由基础设施. 而不是, 已经创建了一个IP基础设施，允许基于IP的视频工作流管道从IP源获取视频, 消除了对专用电缆和设备的需求，这是视频采集和媒体处理的真正成本.

The Live 3.0工作流将提供调度功能，这样广播质量和外部编码的内容都可以用作输入源, 以所需的比特率数进行编码, and muxed (also known as packaging content in multiple formats) into a predefined number of formats. The content can then be protected and 发表 to as many publishing locations as needed, and monitored in real time with automatic error correction capabilities. Operators will simply create workflows as necessary in a matter of minutes, 在活动期间使用它们, 并在不再需要时关闭它们, 释放所有已使用的百家乐软件. Not only will the quality match and perhaps even exceed broadcast TV quality, 但它也将与其可靠性相匹配. 今天,99.99% of live streaming video workflow uptime could be considered unrealistic, 但在未来的几年里, 即使是99.9999%是可行的.

前面的路

In addition to a sophisticated workflow that increases scalability while decreasing costs, 不断变化的直播和点播流媒体世界将需要再次发展，因为包括true在内的重大创新即将出现, 裸眼3D和全息视频. 我们相信Live 3.X将不断发展以应对这些创新, 有效地成为一个“活平台”，使第三方能够从任何设备和任何平台通过api无缝、安全地连接，以构建和运行自己的应用程序. 在这个过程中, 它将拆除目前禁止许多人在网上发布直播活动和直播线性内容的围墙, lighting the spark of innovation in ways hitherto unseen—forever changing the world of digital 媒体.