多格式媒体服务器买方指南

With the plethora of options available for cloud-based delivery and asset management, some streaming practitioners may ask why they should even consider buying a multiformat media server.

这是一个有效的问题. 对于那些只有少量点播视频的人, the use of an online video platform (OVP) such as YouTube could easily suffice. 对于那些想要接触到大量现场观众的人, 内容分发网络(CDN)可能符合要求.

对于那些, 然而, 谁需要在内部和外部传输内容, 教育也是如此, 企业, 甚至还有祭祀市场, 多格式媒体服务器的使用可能就是关键所在.

在今年的买家指南中, we’ll take a look at a few key features you’ll need to know about to make an informed decision.

高清和4K

While the broadcast world and consumer electronics (CE) companies are pushing 4K, we’ll likely be waiting a bit longer for 4K broadcasts than for 4K streaming. 事实上, 4K streams were successfully accomplished for several sporting events during 2013, meaning that media server companies will begin advertising their 4K chops in early 2014.

The difference to remember between high-definition (HD) and Ultra HD (UHD) streaming lies in the fact that the process for HD includes adaptive bitrate (ABR), while the current approach to 4K streams involves single-bitrate streaming via proprietary means. 对高清, the standards are defined for 1080p and 720p in terms of both resolution and audio formats, 但在超高清流媒体领域，我们还没有走到那一步. Caveat emptor when it comes to choosing a future-proof 4K streaming solution.

DASH和HBB

说到1080p, 基于HTTP的动态自适应流(DASH)有了好消息, 至少在DASH-AVC/264的世界里.

版本2.DASH-AVC/264指南的第0条, 支持1080p视频和多声道音频, is now publicly available on the DASH Industry Forum (IF) website (go2sm.com/dash2) and the resulting baselines move upward from 1280x720 progressive (720p) to 1920x1080 progressive (1080p). 除了, the frames per second (fps) rate in the United States is now set at 30 fps, 瞄准H.264 (AVC)渐进式12高调4级.0译码器.

在欧洲和世界其他地区，25fps是版本2的一部分.0规格, meaning that both broadcast and motion picture conversions can be delivered via the DASH-AVC/264 standard as it’s interpreted in the HBB broadcast specifications.

Inquiring minds might be asking about the need for a media server if delivery is provided via HTTP. 答案有三个方面.

First, many legacy devices and players are incapable of playing DASH content. Media servers allow the ability to convert an initial stream into many formats, covering both legacy formats such as RTMP and newer formats such as DASH.

第二个, a number of future devices—such as iOS handsets and tablets—won’t support DASH natively in the foreseeable future, so there’s a need for media servers to enable conversion between formats.

第三, 来实现HTTP传输, 需要在各种分段HTTP格式之间对内容进行分段. 一个好的媒体服务器将以夹层格式保存按需文件, one that can be segmented variously into one or several of Adobe’s HTTP Dynamic Streaming (HDS), 苹果的HTTP直播(HLS), 微软流畅流, 还有一些其他的格式.

这样做的目的是为了保持夹层文件的完整, which is possible now in all HTTP formats—HLS now allows for bit range segmentation—so that the server doesn’t need to deal with storing a vast sea of tiny bits. 在现场现场, 一些媒体服务器使用DASH Live Profile, 允许内容同时流媒体直播到DASH和HLS, 通过使用多路复用(transmuxing).

字幕

媒体服务器提供封闭字幕解决方案, 包括时间文本，如SAMI, SMIL, 定时文本标记语言(TTML, and its less-robust TTML Lite version)—and traditional CEA-608/CEA-708 compliance. Web broadcasters and CE manufacturers alike face a challenge standardizing on common timed-text standards, which means that media servers will play a significant role in converting between the various types of timed text for the foreseeable future. 一些媒体服务器也充当广播播放系统, meaning that closed-caption insertion is a key feature to look for if you plan to broadcast and stream via the same media server.

数字版权管理和加密

Several integrated media servers now integrate with encoders that handle digital rights management (DRM). 当DRM“沿着堆栈向下”移动到编码器时, DRM和加密都可以在摄取点应用, before the source ever leaves the encoder to be sent to the media server. 以这种方式, content can remain encrypted through the ingest and delivery portions of the workflow, 只能在客户端播放器上解码和解密.

除了, as we move closer to a common delivery protocol (HTTP) and a Common File Format (CFF, 基于ISO基础媒体文件格式), 还有一个向通用加密方案(CES)迈进的趋势。. CES将提供使用五种常见DRM方案之一的能力, 和各种媒体服务器支持这五种DRM方案的一个子集.

云计算与本地部署

2013年，基于云的媒体服务器选项有所增加. 所有主流媒体服务器公司都提供以云为中心的服务, 基于事务的转码和媒体交付. 2014年，云将会更加突出, but also significant growth in hybrid solutions that use both on-premise and cloud-based workflows to handle intranet and internet delivery, 分别. The advent of software-defined networking (SDN) will continue to blur the lines between what you buy versus what you lease on a temporal basis.

广告插入和自定义播放列表

Several media servers offer the ability to perform “late binding” functionality, or the ability to keep the audio and video “tracks” of an “online DVD” or stream separate from one another until the last possible moment. 在某些情况下, 这个绑定发生在客户端播放器上, 与媒体服务器保持跟踪哪个音频轨道(e.g.(语言)将与特定的视频流配对. The Common Streaming Format (CSF) based on the ISOBMFF will make late binding a common feature in media servers in 2014.

结论

媒体服务器的选择不仅日趋成熟，而且还在不断扩大. New companies with novel ideas on how to serve content to television-scale audiences are entreating the market. 本文列出了一些需要注意的关键特性. 考虑到选择, the only constant in the buying process for media servers is the need for a well-defined workflow against which to compare different media server product and service offerings.

本文发表在 2014流媒体百家乐软件手册.