Buyers' Guide to Media Servers 2017
2016 saw the rebirth of several older ideas regarding media servers. 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. And if you’re looking to host your media service in the cloud, 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.
Manifest Density
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.
In its simplest form, a manifest—also known as a Media Presentation Description (MPD) in MPEG parlance—is similar to a Spotify playlist, where the end user picks which songs she would like to listen to, and in what order.
The manifest file, 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 multiple data rates and resolutions offered to a device as part of the manifest file.
In addition, as ad-based over-the-top (OTT) video continues to grow as an industry offering, the need to manipulate manifest files grows. As such, the density of the manifest file grows as content publishers look to customize ad playback, multiple data rates, various screen resolutions, and other pertinent metadata necessary to refine ad-serving options to a highly granular level.
Why are multiple data rates offered, not just for the primary content, 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.
From Encode Once to Mix Once
Even with the complexities of manifest density, media servers have grown into the challenge. Most media servers can handle robust manifest files, including the transcoding (codec conversion) or transrating (resolution or data rate downscaling) of a single high-resolution stream. This combination is necessary for proper ABR delivery, 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. But at least one media server company is mixing up that slogan, replacing it with “mix once, play everywhere.”
“Manifest manipulation requires bespoke changes to encoders and origin servers as well as manifest modifications for each and every delivery format, says Arjen Wagenaar, CTO of Unified Streaming, adding that these changes typically use client SDKs that are complicated to maintain.
“There is always that nagging uncertainty: Will players, web browsers, and TVs be able to play the stream from the manipulated manifest?” he asks.
This approach, which the company calls Unified Remix, stitches content upstream from the origin server, creating a reference MP4 file for the company’s origin server (Unified Origin) to access as the source, which is then streamed as a single stream.
This approach to integrating disparate pieces of content, including primary show content and ads, has been around for some time, 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, Unified Streaming 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.”
Old Formats Are New Again
The move toward MP4 files isn’t just limited to one media server company. The ISO Base Media File Format (ISO-BMFF) is the MP4 file container, 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? It turns out that DDVTECH, makers of the MistServer, have approached legacy device streaming in exactly this way for both video on demand (VOD) and live streaming.
“Back at the beginning of 2016 when we released Live MP4, it had a latency of about 2 keyframe intervals,” says Jaron Viëtor, CTO of DDVTECH.
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