April 4, 2017
By Jan Ozer 特约编辑
专题文章

2017 DRM买家指南

如果你打算从主要的美国.S. studios, 您需要加密该内容, which typically means that you’ll have to deploy one or more digital rights management (DRM) technologies. 您将在本文中了解到, while many aspects of the migration from plug-ins like Flash and Silverlight to HTML5 playback have simplified video distribution, 这种转变使得DRM方面更加复杂, 尽管有新的服务和服务模型可以提供帮助.

在进入实现端之前, let’s define DRM, and see what distinguishes it from other less-sophisticated content protection schemes like simple encryption. In essence, DRM有四个组成部分:数字版权管理, encryption, 许可证管理, 和一个支持drm的播放器.

管理数字版权: DRM技术支持广泛的商业模式(包括购买), subscription, rental, and gifting); enable playback on single and multiple platforms via streaming, downloading or side-loading; and provide playback restrictions that guard against or enable playing via HDMI outputs and the like.

Encryption: DRM技术使用加密技术在流之前或流期间保护内容, downloading, 或其他转移.

授权管理: 数字版权管理需要一个数字版权管理平台来管理许可证的申请和发放(Figure 1). 有些还包含域控制器, 哪个管理可以在单个许可下播放内容的多个用户设备, 和计量服务器，跟踪使用数据和总播放为版税目的.

支持drm的播放器: The final element of DRM is a DRM-capable player that can communicate with the DRM platform and enforce all software-and hardware-related playback restrictions. 用于电脑和笔记本播放, some DRMs use an existing plug-in—like Adobe Access and Flash or PlayReady and Silverlight—while other technologies, 比如Google Widevine Classic, 需要单独下载, 这是谷歌停止更新这项技术的原因之一吗. 稍后将详细讨论, the industry is moving from plugin-based DRM to browser-based DRM via the Media Source Extensions (MSE) and Encrypted Media Extensions (EME), 其中DRM必须集成到浏览器中.

在移动设备上，DRM支持可以来自本机浏览器或可下载的应用程序. For example, iOS设备通过Safari浏览器支持苹果的DRM FairPlay, 但如果你是通过自定义应用发行，你也可以使用其他drm. Typically, Smart TVs, OTT boxes, and other consumer electronic devices have one or more DRM technologies pre-integrated into the platform.

在我们深入讨论之前, let’s identify the major DRM technologies and companies on the periphery that provide critical DRM-related functionality.

DRM市场

Let’s start with companies supplying the actual DRM, some of which we’ve already discussed. 与流媒体相关的主要DRM提供商如下:

Adobe Primetime: Adobe’s DRM started its life as Access before Adobe changed the name to Adobe Primetime DRM. 此后，该公司又恢复了Access. 访问主要通过Flash在浏览器中访问, 或者在Mozilla Firefox中使用HTML5, but it is almost exclusive for companies that are also licensing the Adobe Primetime platform.
苹果FairPlay流媒体(FPS): FPS is Apple’s DRM for HTTP Live Streaming (HLS), and it works on iOS, Apple TV, and Safari on OS X. 苹果将FairPlay授权给内容所有者和一些付费平台运营商. DRM供应商可以提供FairPlay加密和许可, 但是它们必须从内容所有者那里获得证书, 谁又能从苹果那里得到呢.
Google Widevine: 有两个版本的Widevine:经典版, 哪些只能通过可下载播放器获得, and Modular, 在Google Chrome和Android设备上使用HTML5. 如前所述，Classic已被弃用. Today, 模块化仅适用于动态自适应流HTTP (DASH), 但很快它可能会在CENC下支持HLS.
DivX: 如今，DivX已被NeuLion收购，在消费电子设备领域有着重要的渗透.
Intertrust马林: 这个开放标准DRM来自Marlin开发人员社区, 是由Intertrust创立的吗, Panasonic, Philips, Samsung, and Sony. 该公司还专注于消费电子设备.
微软PlayReady: PlayReady可以在较旧的浏览器上与Silverlight播放器一起使用, 或者在最新版本的ie浏览器(Windows 8)上使用HTML5.1+)和Microsoft Edge. 它也用于Xbox，以及许多其他智能电视和OTT设备.
Veramatrix VCAS: 这种混合解决方案适用于付费电视分销商，他们也希望将节目分发到电脑上, mobile, and OTT devices.

Surrounding these core DRMs are a number of distribution and technology partners/service providers. As you learned, DRM需要许可功能, 每个DRM供应商提供这些功能的方式不同，有些是直接提供的, 一些有第三方网络, 增值经销商.

许多公司还涉及DRM工作流程, from on-premises and cloud encoding vendors that encrypt the content files to player vendors that help develop video players that talk to the license servers to retrieve the decryption key and play the video file. We’ll look at some of these vendors and discuss how to choose a DRM technology after taking a deeper look at how DRM works.

Fig 1: Components of PlayReady DRM: Note that not all DRM technologies use the concept of domains.

How DRM Works

既然我们已经定义了DRM, 让我们快速了解一下DRM技术的一般工作原理, 从一个名为 DRMtoday. The first step is to get the encryption keys from the DRM provider or create them and upload them to the DRM platform. 这些是用来加密视频的, with the decryption key and associated metadata sent to a license server accessible by the player. 这种加密可以防止在没有解密密钥的情况下回放内容, 通过互联网安全地传输给最终用户.

For most DRMs, external products or services can perform the encryption and packaging shown in Figure 2. 例如，云编码器像 Encoding.com can communicate with a DRM platform to acquire encryption keys to encrypt and package the licensed content, 像Elemental Encoder这样的企业级编码器也是如此, Wowza流媒体引擎, 和Telestream Vantage. In addition, most DRM services provide separate encoding tools to encrypt and package your video and send the key to the DRM Platform. 加密后，受保护的内容被传送到web服务器进行分发.

图2:DRM的第一步是加密. (图片由DRMtoday提供)

当客户播放内容时, 玩家将许可请求发送给内容所有者的代理, 哪个与客户网站上运行的认证过程通信. 一旦客户的网站验证了用户对内容的权利, 代理与DRM平台通信以创建许可证/解密密钥, 然后返回给客户的代理，并最终返回给用户的播放器(Figure 3). 在为离线播放而下载的内容的情况下, 此验证也在下载之前进行, 以及任何播放权和限制.

图3:要播放视频，DRM播放器需要从许可服务器获得解密密钥. (图片由DRMtoday提供)

现在让我们快速了解一下DRM在基于浏览器的环境中是如何工作的, 以及从插件到HTML5的过渡.

从插件到HTML5

In the past, the DRM player was typically a plugin like Flash or a separately downloaded player like Widevine Classic. 在过去的两年里, several standards-based technologies have been implemented to enable the browser itself to function in this role. 虽然单独来看，这些技术在技术上似乎很复杂, as you’ll see, 大局很容易把握. 这些技术包括:

媒体源扩展(mse)

MSE is a W3C HTML Working Group specification for a JavaScript interface to play back media data. Browsers and devices that support MSE can play back chunks of video (or byte-range requests for video segments within a single file), 它可以同时实现自适应比特率流的直播和VOD播放, 配上隐藏式字幕. 而最初的HTML5视频标签支持单个MP4文件的渐进式下载, MSE支持完全自适应流.

HTTP上的动态自适应流(破折号)

DASH is a standardized file format for HTTP-based adaptive streaming that is similar in form and function to Apple’s HLS or Microsoft’s Smooth Streaming. 像所有基于http的自适应流媒体技术一样, there are two types of files in the final output packaging: fragmented video files (or byte-range requests for segments within a single file) and manifest files, which identify the location of the various streams in the adaptive group and the location of the chunks or byte-range requests of the individual segments. In use, most DASH content consists of separate MP4 files (one for each encoded stream in the adaptive group), 和MPD(媒体演示描述)清单文件.

MSE和DASH紧密合作. 也就是说，要播放DASH文件，浏览器或设备必须支持MSE. 所以MSE提供了回放功能, 而DASH是MSE支持的文件格式之一.

加密媒体扩展(eme)

EME is another JavaScript API that enables HTML5based DRM by extending MSE with application programming interfaces (APIs) to control the playback of protected content. EME通过整合所谓的内容解密模块来工作, or CDM, 进入浏览器, device, 或移动操作系统, 允许浏览器或设备直接与许可服务器通信.

通用加密方案(cenc)

CENC details the standard encryption and key mapping techniques used to store the DRM-related data for one or more DRM technologies with the compressed audio/video data. As you’ll see, the ability to manage multiple DRMs is critical because most browsers or other devices will only support one DRM flavor, 使多drm支持成为大多数视频制作人的必需品.

Iso基础媒体文件格式(Iso - bmff)

ISO BMFF is a standardized file format that contains the DASH-encoded video, and CENC DRM metadata. 这些概念结合在一起 Figure 4, a slide from a 这是BuyDRM在2014年流媒体西部大会上的演讲. 左边是ISO BMFF, 其中包含DASHencoded内容和三个DRM的CENC DRM信息. This information is delivered via the cloud to an EME-compatible browser that communicates with the appropriate license server (1, 2, or 3, 但并非全部都是), 并获得解密密钥. 一旦解密，DASH数据就会通过MSE回放.