MPEG DASH Specification is Ratified and Streamlined
The Motion Pictures Experts Group (MPEG) announced last week that the DASH specification has been ratified as a standards-based way to move forward with dynamically adaptive streaming over the HTTP protocol. The DASH specification was approved by 24 national bodies from across North America, Europe, and parts of Asia.
MPEG-DASH, now know as ISO/IEC 23009-1, was frozen technically in August 2011, and ratified by the national bodies prior to MPEG 98 (the 98th meeting of MPEG) held in Geneva, Switzerland, which wrapped up on December 2.
According to a presentation by Thomas Stockhammer of Qualcomm, "editorial updates during MPEG#98 and processing at ITTF [are] such that expected publication of standard in March 2012".
Publication by ISO as an international standard "will take place shortly" according to a press release issued after the close of MPEG 98 in Geneva. Now that DASH has been ratified, at least in its first version, already-high interest is growing as to the companies that will implement the standard. At the Streaming Media West show in early November, a standing-room only crowd listened to members of the MPEG-DASH Promoters' Group espouse the key benefits of DASH and its interoperable potential.
One of those promoters was Akamai's principal architect for media engineering, Will Law, who also replied to a recent commentary by StreamingMedia.com's editor-in-chief, Eric Schumacher-Rasmussen.
"DASH's promise is not an all or nothing proposition," wrote Law in the comment section of the Unified Format or DASHed Hopes commentary. "Today vendors are faced with HLS, HDS, SmoothHD, RTMP, RTSP choice for delivery and support."
"If DASH could help reduce this down to HLS and DASH," wrote Law, "then the convergence that that offers, while not 'total', is none-the-less desirable and beneficial at all levels of the media chain -- encoders, distributors, and playback clients."
The promise of DASH to potentially wean down all dynamic adaptive delivery via HTTP to two types of stream segments -- multiplexed streams using MPEG-2 Transport Stream (TS) or elementary streams using fragmented MP4 files (fMP4) -- is what most interests those on the Promoters' Group.
Another commenter pointed out that the choice is really between the profiles made possible by DASH, namely live and on-demand profiles using fMP4 and those using Transport stream "as DASH/TS and HLS are practically identical in terms of file format."
Even though both DASH's TS profiles and HLS use similar M2TS segments, the differentiating factor is the use of a proprietary manifest file in Apple HLS (known as an .m3u8 file) and an standards-based XML-based manifest file in DASH (known as an MPD or Media Presentation Description file).
"Even just the XML-structure of the DASH MPD offers significant advantages over the limited functionality of M3U8 playlists," wrote Alex Zambelli, Microsoft Media Platform evangelist, in a claim we'll explore in more detail in a future article.
The Future of MPEG DASH
As for next steps in the progression of DASH, three things are in play: first, some additional work will be done on the specification -- set to be addressed prior to the next MPEG meeting, held in San Jose, California, in early February 2012 -- to clarify language in a few areas. In addition, the need for interoperability testing is key missing link as companies begin to build DASH-compliant players capable of playing any or all of the DASH profiles.
Finally, the move to adopt the common file format (CFF) and common encryption schemes must also be completed, the latter providing a multi-DRM (digital rights management) solution in line with the one adopted by the Digital Entertainment Content Ecosystem (DECE) for UltraViolet.
Some work needs to be done here, too, as not everyone's a fan of the five-pronged DRM approach first espoused by DECE for UltraViolet and later adopted by MPEG for consideration as its unified DRM scheme.
On a previous article about DASH ("What Is MPEG DASH?"), highlighting the five DRMs that include Adobe Flash Access, Microsoft Play Ready and an open-source DRM scheme called Marlin, Christopher Levy of BuyDRM.com noted his opinion that the market is only going to accept one DRM scheme.
"Standards are great but the market is going to define where we are all 'going' in the future," wrote Levy. "The studios won't define it alone. The CE manufacturers won't define it. Consumers wont define it. Technology companies won't define it. "
Levy went on to say that Marlin is "dead" and that PlayReady is the DRM scheme that will dominate the market.
"Marlin's not going anywhere," wrote Levy. "Sony dumped it for PlayReady. Sure, FreeVu and Canvas are looking at it. Meanwhile BBC and British Telecom are going with PlayReady. Marlin has no support in the open market. There aren't free video playback platforms like the Microsoft Media Platform available for content owners or licensees to build upon that include Marlin."
Qualcomm's Stockhammer notes, in his presentation, that the "parallel approval process for extensions to ISO Base Media File Format (ISOBMFF) to support DASH 14496-12/AMD 3 and the Common Encryption scheme (IOS/IEC 23001-7)" are forthcoming.
For more on MPEG DASH, view Qualcomm's presentation slides (PDF) from just prior to ratification or this technical whitepaper from Iraj Sodagar of Microsoft, written for the IEEE Computer Society.
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