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Streaming: MPEG-DASH

Admin Globaldots
17.06.2015
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Welcome back to our blog and our sixth appointment with our Streaming Mini Series; it’s been five Articles since we took off on our journey through the Streaming panorama’s complexity and to be totally frank with you – which we are, we barely scraped the surface. We expect another three Articles – including this one – to only round up an Introduction to Streaming as an aspect of Content Delivery.

mpeg-dash

Today’s Article tops the “HTTP Chunked” Streaming Formats landscape and brings us away in the Open Source world, after so much talking about Brand’ed Formats. MPEG-Dash and Progressive Downloads, as we’ll see into our next Article, are the Open Source, cross Technology answer to Brands patenting Formats and capitalizing on it. Not only that: MPEG-Dash has a few key Features which poise it to become the de facto Streaming Format in the next coming years.

For although its Broadcasting Industry’s inception is still second to other Streaming Formats – also from an Encoding Hardware and CDN perspective, there are still some limitations in support -, nothing technically prevents it from spreading wider and one day replace today’s fragmented struggle amongst Apple, Adobe and Microsoft.

Let’s dive into it!

What’s MPEG-DASH?

There comes a point in time when Technology demands consolidation: this can happen due to several reasons.
Solution Providers come up with their own Products which usually address a limited number of people’s needs – typically their own existing Customers. This is one of the reasons why we have Adobe, Apple and Microsoft with their Video Streaming Solutions. Thus far the story is good. But what happens when those same Customers want to taste different formats?

This is where MPEG-Dash came into picture. There was an attempt at consolidation of all Formats leading to a better experience for Users.

A brief history of MPEG-DASH

Video and Audio Content Delivery via Internet began in the late nineteen nineties when the speed of back-then-Internet resembled that of a snail. Microsoft had its Media Player and Standards (and Protocols), and Flash made an entry through Macromedia. Soon Macromedia was consumed by Adobe. In the early days, all Video and Audio content had to be downloaded completely before viewing. This was mandated because of Internet speed limitations and also due to slower, MegaHertz-clocked old fashioned CPUs.

As the Internet became more robust, Video Streaming (defined as a “continuous stream of Video Content”in a Server-Client model) slowly became more feasible; the Video industry put forth its High Definition (HD) Renditions – in the “real” world, the fight was on across DVD and Blue-Ray Discs to contain sharper, deeper copies of a same Movie – and so the Internet Industry agreed on “chunking” Video, Audio and Text channels and deliver them over HTTP as a Transport Protocol.

However, Microsoft came out with its Silverlight and Apple with its HLS Standards. Adobe produced its HDS technology.

At this time, somewhere in 2009, the Content Streaming Industry felt the need to merge all existing Formats into a single Entity and MPEG DASH was born. You must understand that MPEG DASH was an enabler and not a CODEC or technology. The specifications of MPEG DASH were then frozen in mid-2011. The modern, mobile Consumer is more complex, and so Mobile consumption of Video Content has been added to the mix.

How does MPEG-DASH work?

By now, my Dear Reader, you are aware that Adaptive Streaming requires two essential components – Media Files which contain the actual content and the Manifest Files which have the information about the type of content, in the form of Bitrates and Synchronization. In MPEG DASH, the Media Files are called the Media Presentation, while the Manifest File is called the Media Presentation Description.

When a request is made by the Dash Player, the MDP or the Manifest File is first presented. This file contains information on program timing, media content availability, media types, resolutions, minimum and maximum bandwidths, and the existence of various encoded alternatives of multimedia components, accessibility features and required digital rights management (DRM), media component locations on the network, and other content characteristics. Quite some!

The Player selects a suitably encoded Media and starts playing the chosen File. Since HTTP Protocol is used for Transport, streaming of Video becomes now a simpler Operation.

Key Features

The strength of MPEG DASH lies in the following Key Features:

  1. DASH is Codec independent, and therefore will work with any media H.264, WebM and MPEG2TS. This means it can be used for content Encoded following the specs of Apple HLS, Microsoft Smooth Streaming (Silverlight) and also Adobe HDS. This Codec independence is actually the reason why MPEG DASH came into being in the first place.
  2. MPEG DASH supports all DRM or Digital Rights Management methods. This is quite useful when dealing with different – especially if legal – requirements. Since it has Common Encryption and Multiple DRM Support, content can be encrypted once and delivered to the Client supporting various DRM schemes. The supported DRM schemes can be signaled in MPD. Needless to mention, DASH also supports normal track modes for seeking, fast forwards, rewind and the insertion of Advertisements.
  3. The MDP or Manifest File has sufficient information for switching and selecting streams like selecting one Audio stream from different languages, selecting Video between different camera angles, selecting the Subtitles from provided languages, and dynamically switching between different Bitrates of the same video camera.
  4. In MPEG DASH we can have segments with variable duration. This can be especially useful with Live Streaming: the duration of the next segment can also be signaled with the delivery of the current segment.
  5. In MPEG DASH, the same content can be available at multiple URLs. They can be located on different Servers, or delivered by different Sources. The advantage becomes obvious – an End User can stream from any of them to maximize the available Network Bandwidth. This is particularly useful for the largest Broadcasting Entities, which can deliver the always best quality availing on several CDNs (Content Delivery Networks).

Present status and future of MPEG-DASH

What’s of interest to us is the adaptation of MPEG DASH by big Distributors of content. In this context we must note that the chief concern is the availability of DASH enabled Clients. One of the major OTT or Over The Top content Distributors, Netflix, was an early adopter of DASH, even before the specifications were frozen. As a result most applications have used this as a standard. Netflix wants to use DASH primarily for HTML 5 enabled Players.

Netflix actually uses only a subset of the DASH Standard: the ISO Base Media File Format that is used for the Video fragments packaging. The choice is actually driven by the fact that same Media Files are used by a majority of Devices supported by Netflix at present – Television, Set-Top Boxes and Blu-Ray Players. It is finally also worth noting that Netflix does no use of the MDP.

YouTube, another big Video Distributor, has embraced DASH but in a more complex form. It uses a mix of H.264 and WebM based DASH, depending on playback conditions. For Premium content YouTube is using Common Encryption with multiple DRMs.

The future of DASH is also rather tied with Hybrid Broadcast Broadband TV (HbbTV) TV Sets. This is perhaps the most exciting development beyond the VOD environment. Interestingly DASH has emerged as the sole set of Specifications to enable DRM Protected content.

Another area which has to be watched closely is the LTE Broadcast. It is estimated that eighty percent of all Mobile transactions would consist of Video and DASH seems to be making a dash for Mobile Media Delivery.

Conclusion

What started as a consolidation move in the year 2009, MPEG DASH has almost become a major force. Though there are still a few creases to be ironed out, it has largely been accepted as the future of Adaptive Bitrate Streaming. We may see a few clones with different capabilities, but overall, MPEG DASH is a technically sound set of Specifications and Platform and is therefore likely to become a force in the coming days.

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