2011年12月14日
By 蒂姆Siglin 特约编辑
专题文章

批准并简化了MPEG DASH规范

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, 欧洲, 以及亚洲部分地区.

MPEG-DASH, 现在称为ISO/IEC 23009-1, 在2011年8月被严格冻结, and ratified by the national bodies prior to MPEG 98 (the 98th meeting of MPEG) held in Geneva, 瑞士, 12月2日结束.

根据高通公司的托马斯·斯托克哈默的一份报告, "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. 现在DASH已经被批准, 至少在第一个版本中是这样, already-high interest is growing as to the companies that will implement the standard. 在11月初的流媒体西部展上, 一群只能站着的人在听 MPEG-DASH推广小组支持DASH的主要优势及其互操作潜力.

One of those promoters was Akamai's principal architect for media engineering, 将法律, 他也回复了StreamingMedia最近的评论.网站主编埃里克·舒马赫-拉斯穆森说.

"DASH's promise is not an all or nothing proposition,Law写道 in the comment section of the 统一格式或破灭的希望评论. "Today vendors are faced with HLS, HDS, SmoothHD, RTMP, RTSP choice for delivery and support."

“如果DASH可以帮助减少HLS和DASH,Law写道, 以及由此带来的趋同, 虽然不是“全部”, is none-the-less desirable and beneficial at all levels of the media chain -- encoders, 分销商, 播放客户端."

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," 亚历克斯·赞贝利写道, Microsoft Media Platform evangelist, in a claim we'll explore in more detail in a future article.

MPEG DASH的未来

关于DASH进程的下一步, 有三件事在起作用:首先, some additional work will be done on the specification -- set to be addressed prior to the next MPEG meeting, 在圣何塞举行, 加州, 在2012年2月初——澄清一些领域的语言. 除了, 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.

最后, 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.

这里需要做一些工作, 太, 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.

在之前一篇关于DASH (什么是MPEG DASH?"), 突出了包括Adobe Flash Access在内的五个drm, Microsoft Play Ready和一个叫做Marlin的开源DRM方案, Christopher Levy 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,利维写道。. “电影公司不会单独定义它. CE制造商不会定义它. 消费者不会定义它. 科技公司不会定义它. "

Levy went on to say that Marlin is "dead" and that PlayReady is the DRM scheme that will dominate the market.

“马林哪儿也去不了，”列维写道. 索尼为了PlayReady抛弃了它. 当然，免费的Vu和Canvas也在考虑这个问题. 与此同时，BBC和英国电信也在使用PlayReady. 马林在公开市场上没有支持者. There aren't free video playback platforms like the Microsoft Media Platform available for content owners or licensees to build upon that include Marlin."

高通的斯托克哈默指出, 在他的演讲中, 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.

有关MPEG DASH的更多信息，请查看高通的演示幻灯片 (PDF)，在批准本文件之前技术白皮书 from Iraj Sodagar of Microsoft, written for the IEEE Computer Society.