Now that the web vid spec MPEG DASH has been published and interoperability testing is well underway, vendors are starting to put their cards on the table with serious deployments. One of the first to build DASH into products is Thomson Video Networks, which is now supporting it in its ViBE VS7000 multi-screen video platform, with the help of multi-media software company VisualOn. The DASH support is built into VisualOn's multi-media player that Thomson now incorporates into ViBE for cross-platform audio and video playback on target devices.
Just a quick recap on DASH, or Dynamic Adaptive Streaming over HTTP. OTT delivery over unmanaged networks of varying bandwidth to unspecified target devices having a range of display capabilities required a streaming protocol that could cope with congestion, and adapt in real time to changing conditions. It quickly became apparent that dynamic adaptive streaming was the best solution, involving the deconstruction of video files into several sequences or segments, each sequence encoded at a different bit rate. This meant that clients could start streaming video at the highest bit rate they were capable of displaying at the time, subject also to available network bandwidth.
As bandwidth changes, or (less likely) the client device’s capabilities alter because of, say, contention with other applications in the CPU, the stream can switch on the fly to another sequence of video chunks at a different bit rate. Having the video in small chunks enables this switchover to be accomplished quickly and seamlessly, so that at any one time the client is displaying video at the highest bit rate and therefore resolution possible. This enables the "dynamic" aspect of DASH.
One protocol to rule them all
While almost everyone agreed that adaptive dynamic streaming over HTTP was the way forward for OTT and multiscreen delivery, several important variants emerged, all similar but incompatible. The three key ones are Microsoft Smooth Streaming, Apple HTTP Live Streaming, and Adobe HTTP Dynamic Streaming, but there are others, meaning that broadcasters and pay TV operators were faced with having to support a number of parallel streaming protocols. This added to the complication of having to encode at different bit rates as well as supporting various encryption mechanisms and DRMs. Having these multiple competing adaptive streaming technologies was fragmenting the OTT market almost before it began, boosting storage and bandwidth costs, as well as constraining the ability of services to reach all their potential target devices and customers.
There are two other important aspects of DASH: content protection and file structure. Clearly there is no point having a common streaming format without the ability to apply standard encryption capable of interoperating with multiple target DRMs in the client devices. This is accomplished in DASH through Common Encryption, which is also an MPEG standard using AES-128 media encryption. This enables a single protected ISO Base Media file or adaptive streaming presentation to be used with any DRM system supported by a device and the operator or content publisher. Common encryption is also supported by the parallel DECE Ultraviolet standard, which is doing for content downloading what DASH is doing for streaming.
Similarly DASH has adopted the Common File Format (CFF), which again emerged from DECE for Ultraviolet and ensures that the fragmentation process is standardized, so that a single file can be transmitted to all target compliant target devices, and that such devices can themselves interchange the files after receiving them – important for Ultraviolet.
All these capabilities mean that Thomson Video Networks, through integration with VisualOn's OnStream MediaPlayer, can deliver high quality content using MPEG-DASH streaming to most of its target devices, without requiring its customers to build parallel infrastructures for file-based and live encoding for multi-format output.
But this does highlight the continuing issue of Apple’s failure to support DASH. The point here is that all vendors act in their own perceived commercial interest, but some take a broader view of this than others. Microsoft quickly decided that it was in its long term interests to get behind DASH and converge Smooth Streaming towards it.
The final key move came in April 2012 when Microsoft announced that its Media Platform would support DASH, following ratification by ISO/IEC of the standard. But Microsoft had been a key contributor to the development of DASH from the outset, having chaired the MPEG working group, making technical contributions based on its experience with Smooth Streaming. This meant that DASH is quite like Smooth Streaming, using Extensible Markup Language (XML) to describe media presentations in a manifest file referencing media streams stored in ISO Base Media File Format. Therefore it will be easy for Microsoft to merge the two.
Locked out of Apple's garden
DASH is not so far apart from Apple HLS either, but the difference here is that Apple now has a huge base of installed iOS tablets and smartphones and gains significant competitive advantage by keeping control of its ecosystem, and would on the face of it gain little by supporting DASH, or for that matter Ultraviolet. Microsoft on the other hand is just getting into the tablet market and stands to benefit from an industry surge behind DASH. So for now it looks like DASH will fail to deliver unified streaming but will at least bring it down to two.
There are some other issues such as intellectual property and royalties, but these are being resolved, and the main outstanding concern is then convergence with HTML5, the still evolving markup language for presenting multimedia content within browsers. The current working draft of HTML5 still does not specify support for adaptive streaming, or for DRM protection. The main issue is that under HTML5 as it stands a publisher or distributor has no control over how the browser will support access to and present content. There are no standard APIs for ensuring that presentation decisions made by the platform are executed by an application running in the browser.
Copyright © 2012, Faultline
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