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DASH: It's All About Interoperability
At NAB earlier this month, the DASH Talks delved deep into the ways that the standard calls for conformance and allows services like HbbTV to move forward
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“More important than anything else, DASH enables interoperability,” said Iraj Sodagar, a principal multimedia architect at Microsoft and the DASH Industry Forum (DASH-IF) president. “The whole idea of DASH was gathering the best deployed streaming technologies in the market, adding more to it, and creating a standard for interoperability.

The first edition of the core standards were published in April 2012, Sodegar noted. As the MPEG DASH subgroup chair, Sodagar added that “the second edition of MPEG-DASH, which extends the functionality of the first edition, is about to published by ISO/IEC.”

A number of European and U.S. colleagues joined Sodagar on the platform for what was known as DASH Talks, an event that took place earlier this month at during the National Association of Broadcasters show (NAB) in Las Vegas.

One presenter, Bram Tullemans, a senior project manager for technology and innovation at the European Broadcasting Union (EBU), spent time talking about the interleaving of DASH and the hybrid broadband broadcast television standard, or HbbTV.

“What does HbbTV have to do with DASH?” said Tullemans. “In its current form, HbbTV version 1.5, the HbbTV specification prescribes MPEG-DASH for playout of on demand files.”

Tullemans noted that HbbTV version 2.0 was still “in the make” with regards to ratification, but that version 2.0 references the digital video broadcasting (DVB) portion of DASH.

“HbbTV V2 will support both live and on demand playout,” said Tullemans, adding that second-screen synchronisation, using work done in DVB-CSS, also ties DASH and HbbTV together. HbbTV V2 is expected to be finalized in July 2014.

“HbbTV is an ETSI standard describing how DVB broadcast signals can be used to trigger interactive services over internet on connected televisions,” said Tullemans. “It exists due to close cooperation of broadcasters with CE manufacturers. As a result the DASH HTML5 profile is replacing CE-HTML.”

Several of the speakers focused on areas where MPEG-DASH can also be enhanced. Dr. Christian Timmerer, chief information office at bitmovin GmbH talked on the need for DASH reference software and conformance.

“Conformance and reference software serves three main purposes,” said Timmerer, who will be speaking at the 2014 Streaming Forum in London this June. “The first is validation of the written specification and the second is clarification of the written specification."

Timmerer then reiterated Sodagar’s point that DASH is all about interoperability.

“The third purpose of conformance testing,” said Timmerer, is “for checking interoperability for the various applications against the reference software which aims to be compliant with ISO/IEC 23009.”

Conformance against ISO/IEC 23009-2 requires conformance of the media presentation description (MPD), as well as test vectors, DASH access engine reference software, and other sample software.

Timmerer then outlined a number of the conformance components, all of which are available on the video of the DASH Talks that DASH-IF has made available online. One area of particular audience interest would be the media presentation conformance, which handles both MPD validation as well as conformance of segments of ISO Base Media File Format (fragmented MP4) or MPEG 2 Transport Stream (M2TS) against the DASH specification.

Speaking of conformance and validation, the DASH Talks also highlighted the cooperation between the EBU, DASH-IF, and GPAC Licensing, as the three entities have collaborated on a test engine for encoding.

This test engine, according to one of the EBU slides, is a test platform acting as “reference software workflow” for contribution and distribution workflows.

The intent of the platform, which should use only open-source software, is to “facilitate the discussion about suitable MPEG-DASH content generation (including encoding and packaging settings) for different use cases.”

Finally, Dirk Griffioen of Unified Streaming, spoke about two live projects, one using DASH for HEVC with PlayReady support, and the other a streaming radio project for European broadcasters.

Griffioen emphasized the use of other audio formats besides AAC in DASH.

“We spent 2013 focused on the use of DTS-HD Layered audio,” said Griffioen, “and now are exploring the real-time DTS Layered Audio Stream Reconstruction.”

Griffioen explained that the reconstruction process allowed a single, high-quality stream to be converted into multiple bitrates of lower-bandwidth audio streams, including surround sound, for use in both Apple’s HTTP Live Streaming (HLS) and Microsoft Smooth Streaming.

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