媒体服务器买家指南2017

2016年见证了一些关于媒体服务器的老想法的重生. Whether it was the marriage of multichannel encoders and a media server integrated into the same chassis or a method for legacy formats to stream to both legacy and modern devices, the core features of media server software continue to expand to handle mainstream and fringe use cases.

The following highlights of the past year cover just a few key things to consider when making a buying decision regarding media server software. 如果你想在云端托管你的媒体服务, or you want to use a managed service instead of buying the media server software outright, you’ll be glad to know that all of the companies mentioned in this Buyers’ Guide offer options as flexible as your budget.

明显的密度

If the problems of years past centered on converting one streaming protocol to another—from RTMP, say, to Apple HTTP Live Streaming (HLS) or Smooth Streaming—the new challenge is how to handle frequent changes to the manifest file required by scalability challenges and changing network infrastructure environments.

A manifest file acts as a stated playlist for the end-user’s video player to follow from one piece of content to another. The file itself is often text or extensible markup language (XML) for ease of readability by both a human engineer and the media server(s) required to serve up content listed on the manifest file.

最简单的形式, a manifest—also known as a Media Presentation Description (MPD) in MPEG parlance—is similar to a Spotify playlist, 最终用户在哪里选择她想听的歌曲, 以什么顺序.

清单文件, though, is invisible to the user and contains more than just the songs chosen for playback. Both manifests and MPDs contain information about media segments—the chunks of data that make up Apple HTTP Live Streaming (HLS) or MPEG Dynamic Adaptive Streaming over HTTP (MPEG-DASH)—as well as information necessary to choose between the 多种数据速率 and resolutions offered to a device as part of the manifest file.

In addition, 基于广告的OTT (over-the-top)视频作为一种行业产品继续增长, 操作清单文件的需求在增长. As such, the density of the manifest file grows as content publishers look to customize ad playback, 多种数据速率, 各种屏幕分辨率, and other pertinent metadata necessary to refine ad-serving options to a highly granular level.

为什么提供多个数据速率, 不仅仅是主要内容, but also for the ads served alongside the user-chosen premium content in her individualized playlist?

The primary reason is user feedback: Consumers would rather watch or listen to streamed content at lower bitrates than wait for the content to buffer (or play haltingly) at higher data rates. The ability to adapt a stream to the current realities of network congestion or intermittent delivery is know as adaptive bitrate (ABR) streaming, and it adds a high level of complexity and density to any particular manifest file.

从编码一次到混合一次

Even with the complexities of manifest density, media servers have grown into the challenge. 大多数媒体服务器都可以处理健壮的清单文件, including the transcoding (codec conversion) or transrating (resolution or data rate downscaling) of a single high-resolution stream. 这种组合对于适当的ABR递送是必要的, especially for live content that’s streamed from the acquisition point as a high bitrate/high resolution such as 4K that needs to be downscaled to 1080p or even 720p for streaming delivery.

The industry slogan for this has been “encode once, stream everywhere” for several years now. 但至少有一家媒体服务器公司混淆了这一口号, 用“混合一次”代替, 到处玩.”

“Manifest manipulation requires bespoke changes to encoders and origin servers as well as manifest modifications for each and every delivery format, Arjen Wagenaar说, CTO of 统一的流, adding that these changes typically use client SDKs that are complicated to maintain.

“总会有一些不确定因素:意志玩家, web browsers, 电视可以播放操纵舱单上的数据流?” he asks.

This approach, 该公司称之为“统一混音”, 从原始服务器向上游缝合内容, creating a reference MP4 file for the company’s origin server (Unified Origin) to access as the source, 然后将其作为单个流传输.

这种集成不同内容的方法, 包括主要节目内容和广告, 已经有一段时间了吗, but only recently has it found its way into media server applications that the general public can buy to stream to a wide variety of devices. In essence, 统一的流 is manipulating the streams rather than the manifest file so that “the stream functions as though it has a single origin and a single timeline.”

旧格式又新了

向MP4文件的转变不仅仅局限于一家媒体服务器公司. ISO基础媒体文件格式(ISO- bmff)是MP4文件容器, and this is key to being able to stream fragmented MP4 (fMP4) using byte-range addressing without the need to create hundreds, thousands, or even hundreds of thousands of standalone segments or chunks before streaming commences.

But what about streaming actual MP4 files, in a way that allows legacy devices to receive streams? 事实证明，DDVTECH的制造商 MistServer, have approached legacy device streaming in exactly this way for both video on demand (VOD) and live streaming.

“回到2016年初，当我们发布Live MP4时, 它有大约2个关键帧间隔的延迟,Jaron Viëtor说, DDVTECH的首席技术官.