2016年12月2日
By 1月时特约编辑
专题文章

Containing Costs: How Publishers Can Save Money on ABR 编码

让我给你几个数字. 第一个显示在图1,从编码.com’s 《百家乐软件》 2015年云编码服务产生的自适应比特率(ABR)格式的份额分别是多少. 如图1所示, HTTP 在线直播 (HLS) dominates with 71 percent, 光滑的流 is second with 19 percent, and 动态 Adaptive Streaming over HTTP (破折号) is third with 10 percent.

I hear you thinking, “光滑的流 is second? All I hear about is 破折号, 破折号, 破折号 (and more 破折号).” Yes, 光滑的流 is second, which leads to the second number. 这是, 就在最近的2014年, 在微软Xbox等游戏机上观看Netflix的观众比例, 索尼PlayStation, 或者任天堂Wii 合计43%. Though this number has clearly dropped since then, 编码.com’s report attributes the 光滑的流 number to the Xbox One, ，它已经超越了游戏主机，成为传递内容的主要手段, 包括OTT订阅.”

这是什么意思?? 如果你在分发优质内容, you probably should support two if not three ABR technologies. And even if you’re distributing free content for training, 销售, 市场营销, 或者其他目的, you’ll probably also have to support multiple ABR formats sometime in the future. 正如您将在本文中读到的, there’s an expensive way to support multiple ABR formats, 一种廉价的方式. It’s your money; give me a few minutes and I’ll show you how to save a bundle.

图1. 由编码产生的ABR格式的份额.2015年

技术背景

Let’s start with everyone on the same page. All videos, live and VOD, start with a single file. 自适应地交付此文件, 我们以不同的分辨率和数据速率创建该文件的多个版本，以适合传输到一系列播放设备. This group of files is often referred to as an encoding ladder.

All HTTP-based adaptive bitrate technologies like HLS, 破折号, 和平滑流媒体使用存储在特定容器格式的视频，带有清单文件，可以为播放器识别这些文件的位置. HLS使用存储在MPEG -2传输流格式(TS文件)中的文件以及M3U8清单文件. 平滑流使用碎片化的MP4文件存储在ISMV格式与ISM清单文件. 破折号使用单个或多个MP4文件存储在MP4格式与MPD清单文件. 完成图片, Adobe基于HTTP的动态流媒体(HDS)使用F4F格式存储的碎片MP4文件, 与F4M清单文件.

Note that when HTTP-based adaptive streaming originated, each file in the encoding ladder had to be broken into separate chunks, 通常是4到10秒, which created an administrative and storage nightmare. 因为他们, 所有ABR技术都包含了以正确的ABR格式处理单一源视频文件的能力, retrieving segments from that file via byte-range requests from the player. 而不是检索一个特定的块, the player retrieves a specific segment from the single file, simplifying file creation and distribution.

The important thing to recognize is that you can use a single set of encoded H.264 files as the source for all ABR formats. 也就是说，一旦你有了H.将264文件编码到编码阶梯中，将它们打包成多种ABR格式是很简单的. 这显示在图2，来自微软Azure网站.

图2. 从一组编码文件创建多个ABR打包(图片来自Microsoft Azure网站).

左边是单个输入文件, 然后被编码成多个文件, 通常是MP4格式. 然后将这些文件转换为特定ABR技术所需的容器格式(如果需要的话)。, 并创建清单文件, 这一过程通常被称为转化. 图中显示了多个MP4文件打包成HLS和光滑的流格式, but the same schema works with 破折号 and HDS. 基本上, once you have the encoded multiple-bitrate MP4 files, the hard work is done; transmuxing is a relatively lightweight operation that can be performed very quickly and efficiently.

到目前为止, so good; you have the multiple files packaged in the ABR format necessary for delivery to your target player. 有什么不好的? 好吧, 回想一下我们最初的前提, the need to deliver using three ABR packages— HLS, 光滑的流, 和冲. If you create all three packages and upload them to the cloud for delivery, you just tripled your monthly storage costs. 雪上加霜, 如果你在云端编码, you also may have tripled your encoding costs. 举个例子, the Amazon Elastic Transcoder can produce 破折号, HLS, 和平滑流ABR封装, 但是如果你使用这个服务, you’ll pay the normal rate three times for the privilege.

OK, 你明白了:花钱让云编码器生成多个ABR包并将它们全部存储在云中可能不是最明智的举措. 另一种选择是什么? 动态打包.

交付:静态vs. 动态

动态包装, 创建多比特率MP4文件并将其上传到流端点，如图所示图3. As different players request chunks or byte-range requests in the video, 服务器检索MP4文件, 转换为必要的ABR格式, 并将其发送给玩家. 而块可能临时存储在内容交付网络的HTTP缓存结构中的某个地方, they are never stored on the streaming server, so you’re charged simply for the stored MP4 files. Since the server creates the ABR packaging dynamically, you’re never charged for that operation by your cloud encoder.

图3. 动态打包 (Image from Microsoft Azure website)

即使对视频应用数字版权管理，也可以执行动态打包, or if you need to apply different caption formats for your target players. In most instances, there are few, if any, meaningful downsides.

动态使用微软Azure

I’ll start with Microsoft Azure, the source of Figures 2 and 3. 在这里，我采访了Martin Wahl，全球客户参与的首席项目经理. 根据沃尔的说法, though the Azure cloud encoder was formerly able to produce static packaging, 该公司不赞成这种功能，因为微软敦促其客户动态而不是静态地创建他们的包装.

成本? 基本上, it’s included in the cost of distribution. 根据沃尔的说法, Azure的, you can stream directly from the origin server, 或者使用Azure CDN, which adds points of presence (POS) at the edge, 和缓存, which should improve the overall quality of experience of your viewers. Both services charge by the gigabyte delivered, 在每种情况下, 动态打包, 包括字幕和加密, 包括. Or, 您可以将打包的ABR视频从原始服务器发送到第三方CDN, in which case you’ll pay for the transfer bandwidth to the CDN, 动态包装也包括在内.

微软为HLS的直播和VOD播放提供了免费的Azure媒体播放器, 破折号, or 光滑的流 formats with fallback to Flash or Silverlight. 微软可以为PlayReady或Widevine提供许可密钥，但需支付少量额外费用，或者向提供该服务的一系列第三方提供商提供访问权限.

在讨论动态包装带来的成本节约时，沃尔指给我看了一个 Azure站点的案例研究描述了日本优质内容平台Rakuten ShowTime如何使用Azure简化其分发工作流程并降低成本. 乐天的报价超过了120张,000个视频，用于发送到智能电视, 个人电脑, 智能手机, 平板电脑, 游戏平台. 迁移到Azure平台之前, 该服务在光滑的流中创建并存储每个游戏的单独迭代, HDS, HLS, 还有其他一些, 经常为不同的DRM技术创建这些ABR格式的多个迭代.

In 2013, the number of discrete files managed exceeded 100 million, which was the limit of Rakuten’s on-premises storage management system. This prompted a move to the cloud, and discussions with Microsoft Azure. 乐天最终在2015年转向动态包装，并发现了三个关键优势. First, Rakuten’s storage cost was “reduced to 25 percent of what it was before.“第二, 该公司能够更快地推出新游戏，因为它不再需要进行多次迭代. 第三, since the number of output files was dramatically reduced, the company could more easily find and resolve file-related issues, which Rakuten stated cut management costs by “as much as 60 percent.”

Wowza是如何运作的

第一个(如果不是第一个)提供传输功能的是Wowza Media Systems, 它为diy提供Wowza流媒体引擎，为那些想要托管服务的人提供Wowza流媒体云. Wowza的定价因产品而异, 但你可以从每月65美元的Wowza流媒体引擎订阅开始. Wowza流媒体云的计划从单一的现场活动到24/7的广播, and both products can deploy using the new Wowza Player.

就像蔚蓝的, both Wowza products can accept a single live input stream, convert that to multiple bitrate MP4 files, and then package these files for different display devices on-the-fly (图4). 另一种选择, “老式”的多格式传输需要昂贵的硬件编码器在现场创建流和包, and sufficient bandwidth to get these streams out of the building in real time. 编码器的成本和带宽的节省使得实时转码和动态包装的结合对现场活动生产者来说是一个灌篮.