2016年12月2日
By 1月时特约编辑
专题文章

控制成本:出版商如何在ABR编码上省钱

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》 which shows the respective share of the adaptive bitrate (ABR) formats produced by the cloud encoding service in 2015. 如图1所示, HTTP直播(HLS)以71%的份额占据主导地位, 光滑的流以19%的支持率位居第二, 基于HTTP的动态自适应流(破折号)排名第三，占10%.

我听到你在想，“流畅是第二? 我听到的都是破折号, 破折号, 破折号(还有更多的破折号).“是的，平滑流是第二个，这导致第二个数字. 这是, 就在最近的2014年, the percentage of viewers watching Netflix on gaming consoles like Microsoft Xbox, 索尼PlayStation, 或者任天堂Wii 合计43%. 虽然从那以后这个数字明显下降了，编码.com的报告将平滑流媒体的数量归因于Xbox One, “which has evolved beyond a game console to become a leading means of delivering content, 包括OTT订阅.”

这是什么意思?? 如果你在分发优质内容, 你可能应该支持两种(如果不是三种)ABR技术. 即使你在分发免费的培训内容, 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, 有一种昂贵的方法来支持多种ABR格式, 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

让我们从每个人都在同一页开始. 所有视频，直播和视频点播，从一个文件开始. 自适应地交付此文件, we create multiple renditions of that file at various resolutions and data rates suitable for delivery to a range of playback devices. 这组文件通常被称为编码阶梯.

所有基于HTTP的自适应比特率技术，如HLS, 破折号, and 光滑的流 use video stored in specific container formats with manifest files that identify the locations of those files for the player. HLS uses files stored in the MPEG-2 transport stream format (TS files) along with M3U8 manifest files. 光滑的流 uses fragmented MP4 files stored in the ISMV format with ISM manifest files. 破折号 uses single or multiple MP4 files stored in the MP4 format with MPD manifest files. 完成图片, Adobe’s HTTP-based 动态 Streaming (HDS) uses fragmented MP4 files stored in the F4F format, 与F4M清单文件.

请注意，当基于HTTP的自适应流开始时, 编码阶梯中的每个文件都必须分成单独的块, 通常是4到10秒, 这会造成管理和存储方面的麻烦. 因为他们, all ABR technologies have incorporated the ability to work with a single source video file in the correct ABR format, 通过来自玩家的字节范围请求从该文件中检索片段. 而不是检索一个特定的块, 播放器从单个文件中检索一个特定的片段, 简化文件的创建和分发.

重要的是要认识到，您可以使用一组编码的H.264文件作为所有ABR格式的源. 也就是说，一旦你有了H.264 files encoded into the encoding ladder, it’s trivial to package them into multiple ABR formats. 这显示在图2，来自微软Azure网站.

图2. Creating multiple ABR packaging from a single set of encoded files (Image from Microsoft Azure website).

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. These files are then converted into the container format required by the specific ABR technology (if necessary), 并创建清单文件, 这一过程通常被称为转化. The figure shows the multiple MP4 files packaged into HLS and 光滑的流 formats, 但同样的模式也适用于破折号和HDS. 基本上, 一旦你有了编码的多比特率MP4文件, 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, 需要使用三个ABR包交付- HLS, 光滑的流, 和冲. 如果您创建了所有三个包并将它们上传到云中以便交付, 你每月的仓储费增加了两倍. 雪上加霜, 如果你在云端编码, 您还可能使编码成本增加了三倍. 举个例子, 亚马逊弹性转码器可以产生破折号, HLS, 和平滑流ABR封装, 但是如果你使用这个服务, 你要付正常利率的三倍.

OK, you get it: Paying your cloud encoder to produce multiple ABR packages and storing them all in the cloud might not be the most financially prudent move. 另一种选择是什么? 动态打包.

交付:静态vs. 动态

动态包装, you create the multibitrate MP4 files and upload them to a streaming endpoint as shown in 图3. 当不同的玩家请求视频中的块或字节范围请求时, 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. While the chunk may be temporarily stored somewhere in the content delivery network’s HTTP caching structure, 它们永远不会存储在流媒体服务器上, 所以你只需要为储存的MP4文件付费. 因为服务器动态创建ABR封装, 您的云编码器永远不会对该操作收费.

图3. 动态打包(图片来自Microsoft Azure网站)

You can perform 动态打包 even if you are applying digital rights management to your video, 或者如果你需要为你的目标玩家应用不同的字幕格式. 在大多数情况下，如果有的话，几乎没有什么有意义的缺点.

动态使用微软Azure

我将从Microsoft Azure开始，即图2和图3的来源. Here I spoke with Martin Wahl, principal program manager for global customer engagement. 根据沃尔的说法, 尽管Azure云编码器以前能够生成静态打包, the company is deprecating that capability as Microsoft urges its customers to create their packaging dynamically rather than statically.

成本? 基本上，它包含在分销成本中. 根据沃尔的说法, Azure的, 您可以直接从原始服务器进行流传输, 或者使用Azure CDN, 它在边缘增加了存在点(POS), 和缓存, 哪一种方法可以提高观众的整体体验质量. 这两种服务都是以gb为单位收费的, 在每种情况下, 动态打包, 包括字幕和加密, 包括. Or, you can send the packaged ABR videos from the origin server to a third-party CDN, 在这种情况下，您将支付传输带宽到CDN, 动态包装也包括在内.

Microsoft offers the license-free Azure Media Player for live and VOD playback of HLS, 破折号, 或平滑流格式，退回到Flash或Silverlight. Microsoft can supply license keys for PlayReady or Widevine at a small extra charge or provide access to a range of third-party providers of this service.

Discussing the costs savings delivered by 动态打包, Wahl pointed me toward a Azure站点的案例研究 that describes how Japanese premium content platform Rakuten ShowTime used Azure to simplify its distribution workflow and cut costs. 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, the service created and stored separate iterations of each title in 光滑的流, HDS, HLS, 还有其他一些, oftentimes creating multiple iterations of these ABR formats for different DRM technologies.

In 2013, 管理的离散文件数量超过1亿个, 乐天内部存储管理系统的极限在哪里. 这促使他们转向云计算，并与微软Azure进行了讨论. Rakuten ultimately switched to 动态打包 in 2015, and it found three key benefits. 首先，乐天的仓储成本“降到了以前的25%.“第二, the company was able to offer new titles faster because it no longer had to produce the multiple iterations. 第三, 因为输出文件的数量大大减少了, 公司可以更容易地发现和解决与文件相关的问题, 乐天表示，这将使管理成本降低“多达60%”.”

Wowza是如何运作的

One of the first (if not the first) to offer transmuxing capabilities was Wowza Media Systems, which offers the Wowza Streaming Engine for DIYs and the Wowza Streaming Cloud for those who want a managed service. Wowza的定价因产品而异, but you can start with a subscription for the Wowza Streaming Engine for $65/month. Wowza Streaming Cloud has plans ranging from single live events to 24/7 broadcasting, 这两款产品都可以使用新的Wowza Player进行部署.

就像蔚蓝的, 两款Wowza产品都可以接受单个实时输入流, 将其转换为多比特率MP4文件, 然后将这些文件打包到不同的显示设备上(图4). 另一种选择, “old-style” of multiple format delivery required expensive hardware encoders at the live site to create the streams and packages, and sufficient bandwidth to get these streams out of the building in real time. The encoder cost and bandwidth savings make the combination of real-time transcoding and 动态打包 a slam dunk for live event producers.