DASH-AVC/264: Paring Down MPEG-DASH
The DASH Industry Forum (DASH-IF) announced today the completion of a pared down version of DASH profiles known as DASH-AVC/264.
When MPEG-DASH was ratified back in late 2011, it piqued a great deal of intereste and was seen as the culmination of an industry push to standardize on a single adaptive bitrate (ABR) technology to speed the adoption of HTTP-based video delivery.
Yet, within the MPEG-DASH specification, there were several potential container formats and profiles intended to accommodate industry realities: both MPEG-2 Transport Stream (M2TS) and fragmented MP4 (fMP4) were accommodated within DASH to cover then-current ABR implementations, respectively, from Apple and everyone else.
DASH-IF's move to pare down the MPEG-DASH standard to a few fMP4-based profiles allows the industry to focus on the growing popularity of fMP4 delivery for over-the-top (OTT) use cases as the consumer electronics industry creates DASH-compliant set-top boxes.
"DASH-IF's efforts on defining clear and clean DASH-based interoperability points enables vendors and service providers to build and deploy interoperable products and services that work with each other out of the box,” says DASH-IF chairman Iraj Sodagar.
DASH-IF has identified what it calls "interoperability points" that use AAC as the audio codec, AVC as the video codec (also known as H.264 or MPEG-4 Part 10), and fMP4 as the base container format. The latter is better known as the ISO Base Media File Format (ISOBMFF).
The primary interoperability point is designed around high-definition (HD) video up to 720p at the AVC Progressive High Profile.
"The scope of this interoperability point is the basic support high-quality video distribution over the top," states a pre-release version of the DASH Industry Forum's "Guidelines for Implementation: DASH264/AVC Interoperability Points" which will formally be released today.
In addition to DASH-specific constraints, such as the elimination of playlist-based addressing and open Group of Pictures (Open GoP) switching, DASH-IF says that the new DASH-AVC/264 also adds restrictions on media codecs and other technologies.
"The codec considered for basic video support up to 1280 x 720p at 30 fps is H.264 (AVC) Progressive High Profile Level 3.1 decoder," the document states. "This choice is based on the tradeoff between content availability, support in existing devices and compression efficiency."
However, DASH-IF also recognizes that we live in a world that's still split between high-definition and standard-definition.
"In addition, it is recognized that certain clients may only be capable to operate with H.264/AVC Main Profile Level 3.0," the pre-release document states. "Therefore content authors may provide and signal a specific subset by providing a dedicated interoperability identifier referring to a standard definition presentation. This interoperability point is defined as DASH-AVC/264 SD."
Both live and on-demand profiles are supported. DASH-IF's expectation is that a client (player) implementation, besides supporting H.264 720p Progressive High Profile will also "support at least presentation of stereo audio (based on HE-AAC v2 Profile, basic subtitles (based on ISO/IEC14496-30), and basic support for encryption/DRM (based on ISO/IEC 23001-7)".
While there are a number of current claims in the marketplace, some of which refer to support for DASH264, today's release of the interoperability points also solidifies the official naming as DASH-AVC/264. Going forward, there may still be references in the marketplace to DASH264, but these references are merely shortened names for DASH-AVC/264.
Further information regarding these implementation points can be found on the DASH-IF website.
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