DASH: A Universal Standard for Streaming Video Content to Multiple Devices

Monday, May 14, 2012

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Dynamic Adaptive Streaming over HTTP
Using the DASH standard, an operator would only package, store, and deliver one piece of content one time, realizing significant cost savings. In this case, the savings are expected to be between two to three times more than when using the current proprietary approach.

Consumers now have the capability to watch a live NCAA basketball game on a smartphone or stream a high-definition movie on an iPad, but for content providers like Netflix, delivering that streaming content isn’t so easy. Thierry Fautier, Senior Director of Convergence Solutions at Harmonic Inc takes a look at how Dynamic Adaptive Streaming over HTTP can help.

A multitude of adaptive bit rate formats using HTTP as the underlying delivery method —including Apple® HLS, Microsoft® Smooth Streaming, and Adobe® HDS — create a painful challenge for content delivery operators who must separately encode, store, and transport each piece of video content in order to be compatible with all three formats. This costly, time-consuming process creates a scalability issue for operators and, in turn, reduces the quality of streaming video content for end users.

To resolve the frustrations associated with multiple HTTP delivery platforms, the industry recognized the need for a unified format capable of delivering streaming video content to connected devices, and in 2009, the Moving Picture Expert Group (MPEG) issued a call for proposal for an HTTP streaming standard. Over the next two years, MPEG developed the best specification – called Dynamic Adaptive Streaming over HTTP (DASH) – and a new protocol was born, providing a single delivery format for efficient, high-quality streaming of multimedia content over the Internet.

What is DASH?
DASH is an ISO standard that addresses the increase of Internet video by providing a universal delivery format, enabling operators to cost-effectively scale adaptive streams to any connected device using a common encryption technology with one master key. By utilizing a single encryption standard, content is encrypted once and streamed to clients that support various digital rights management (DRM) systems. Each client receives a set of decryption keys and other necessary information using its specific DRM system, which is signaled in the DASH protocol, and then has the capability to stream the commonly encrypted content from the same server.

DASH can be implemented across all content delivery vehicles –broadcast, mobile, interactive television, and the Internet – while providing interoperability between all DASH profiles and connected devices. This level of interoperability is not currently fully offered with any of the three popular streaming formats today (see Table 1).

 

Features

Apple HLS

Microsoft Smooth  Streaming

Adobe HDS

DASH

Codec used

H.264

H.264, VC-1

H.264, VP6

H.264  or other MPEG codec family (SVC, MVC, HEVC)

Open standard

No

No

No

Yes

Adopted by industry consortium

No

No

No

Yes

Subtitle support

Partial

Yes

Partial

Yes

Multiple audio support

V4 only

Yes

Yes

Yes

Interoperability testing

No

No

No

Yes

Trick mode support

Partial

Yes

Partial

Yes

CDN friendly

Requires chunk carriage optimization

Requires specific IIS-7 origin

Requires specific FMS origin

Yes

Device support

IOS, Mac, Xbox, Playstation, STB, TV Android

PC, Xbox, STB, TV

PC, TV

Limited in 2012

Common encryption

No

No

No

Yes

Licensing

Unknown

Unknown

Unknown

ISO policy

 

The DASH protocol provides content operators with a more streamlined method for streaming content delivery by enabling:

  • reuse of existing technologies, such as containers, codecs, and encryption
  • deployments on top of HTTP content delivery networks (web infrastructures, caching)
  • high-quality user experience (low start-up, no rebuffering, trick modes)
  • live, on-demand, time-shift optimized for content delivery networks
  • addressing of global and regulatory deployment issues (multiple audio tracks and subtitles)
  • multi-DRM support 
  • convergence with existing proprietary technologies 

How DASH Works
The DASH protocol consists of two parts: the Media Presentation Description (MPD), which describes a manifest of the available content, its alternatives, their URL addresses, and other characteristics; and segments, which contain the actual multimedia bit streams in the form of single or multiple files.

When an operator receives content, it goes through a multi-step process before being delivered to end users (see Figure 1). First, an encoder receives an input source and generates multiple adaptation sets and representations (e.g. video with different qualities, audio with different languages). Next, the encoder performs splicing of all representations and generates the MPD files correspondingly. The encoder publishes the spliced content and MPD files to HTTP servers, and then the DASH client downloads the MPD in order to retrieve a complete list of components, including video, audio, and closed captions. The DASH client then determines the preferred set of representation based on its capability (e.g. resolution), user preference (e.g. audio language), and network bandwidth (e.g. high or low bitrate). And finally, the DASH client downloads the desired spliced content from the HTTP server and plays the content.


Fig. 1: DASH Streaming Process

An Application of DASH 
Let’s examine a real-world application where DASH enables an operator to more efficiently deliver streaming media content. Typically, an operator today publishes video content on an iPad using Apple HLS, on an Xbox® with Microsoft Smooth Streaming, and on a PC using the Adobe HDS format. In preparing content for three separate streaming formats, the operator incurs three times the packaging cost, three times the storage cost, and three times the delivery cost. More optimized techniques can be applied to unite the storage and the CDN traffic, but this calls for either more processing cost or the use of more proprietary techniques. Using the DASH standard, an operator would only package, store, and deliver one piece of content one time, realizing significant cost savings. In this case, the savings are expected to be between two to three times more than when using the current proprietary approach. And, of course, this leaves  the operator full latitude to choose from any DASH supplier. The decrease in CDN traffic increases an operator’s available bandwidth, and as storage can be decreased at the edge, edge caches can be pushed further into the network, providing the end user with a higher quality streaming video experience.

Most of an operator’s existing content and production equipment is compatible with DASH. To utilize the DASH protocol, an operator must upgrade existing servers that rely on HTTP protocols such as Microsoft Smooth Streaming, Apple HLS, and Adobe HDS with DASH streaming capability. Other existing technologies such as encoders also require a software upgrade of the packaging in order to be compatible with the new universal standard. Additional upgrades would occur on the client side, where browsers such as Google Chrome and Internet Explorer must be modified to support DASH. The MPEG DASH transition is very much a software upgrade of existing deployed adaptive streaming technologies, which makes it extremely attractive. 

With regards to data format, Apple HLS content is similar to the DASH M2TS main profile, while  Microsoft Smooth Streaming and Adobe HDS content are similar to  the DASH ISOBMFF Live profile.

The Future of DASH
As a new international standard, DASH has the capability to evolve over time, however, committees such as 3GPP, HbbTV, and DECE — which have shown interest to support DASH since it is the only international standard for adaptive streaming — still need to define the relevant profiles for their targeted applications. Some of today’s connected TVs and tablets connect to broadcast services such as HbbTV as well as video-on-demand services such as Ultra Violet; therefore, it is important to define cross profiles and application interoperability. 

A consortium called the DASH Promoters Group (www.dashpg.com), tasked with supporting the DASH standard, is helping define the cross profiles and applications. Founded by Microsoft, Netflix, and Qualcomm, the DASH Promoters Group is supported by roughly 20 leading technology companies in the multimedia video industry, most of whom have collaborated to define the DASH protocol. Recently, the first broadcast organization— EBU (European Broadcaster Union) — joined the group, and more members of the HbbTV (Hybrid Broadband Broadcast TV) community are expected to support the DASH protocol, as HbbTV 1.5 will specify DASH for Connected TVs. DASH is currently being considered by other standards groups, such as the Third Generation Partnership Project (3GPP) and the Digital Entertainment Content Ecosystem (DECE).

European countries, such as Italy and France, are deploying DASH for their connected TV markets this year, and Spain is expected to follow soon after. During these trials, the interoperability between standardized profiles (broadcast and video on demand) and a wide variety of devices (beginning with television) will be tested to pave the way for commercial deployments with a broader range of devices such as PCs, tablets, and smartphones, which is expected to take place next year, followed by a mass deployment of DASH technology in 2014.

Conclusion
DASH and its related specifications have been published by ISO as an International Standard. In the meantime, the DASH Promoters Group will continue to support the universal format. This month at the National Association of Broadcasters tradeshow in Las Vegas, the group will demonstrate the universal protocol through a live video stream encoded by Harmonic, ingested to Akamai’s content delivery network, and delivered to a Qualcomm processor-based Android™ mobile tablet for playback, as well as DASH VOD interoperability on other devices such as PC client from Intertrust and Connected TV from Samsung. These live demonstrations will showcase how a unified format not only enables efficiency and cost savings for content and service  providers, but most importantly, how those efficiencies and cost savings ultimately trickle down to consumers, who will experience a faster, higher-quality streaming video experience on any viewing device.

 

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