Dynamic Adaptive Streaming over HTTP

Dynamic Adaptive Streaming over HTTP (DASH), also known as MPEG-DASH, is an adaptive bitrate streaming technique that enables high quality streaming of media content over the Internet delivered from conventional HTTP web servers. Similar to Apple's HTTP Live Streaming (HLS) solution, MPEG-DASH works by breaking the content into a sequence of small HTTP-based file segments, each segment containing a short interval of playback time of content that is potentially many hours in duration, such as a movie or the live broadcast of a sports event. The content is made available at a variety of different bit rates, i.e., alternative segments encoded at different bit rates covering aligned short intervals of play back time are made available. While the content is being played back by an MPEG-DASH client, the client automatically selects from the alternatives the next segment to download and play back based on current network conditions. The client selects the segment with the highest bit rate possible that can be downloaded in time for play back without causing stalls or re-buffering events in the playback. Thus, an MPEG-DASH client can seamlessly adapt to changing network conditions, and provide high quality play back with fewer stalls or re-buffering events.

MPEG-DASH is the first adaptive bit-rate HTTP-based streaming solution that is an international standard. MPEG-DASH should not be confused with a transport protocol — the transport protocol that MPEG-DASH uses is TCP.

MPEG-DASH uses existing HTTP web server infrastructure that is used for delivery of essentially all World Wide Web content. It allows devices like Internet-connected televisions, TV set-top boxes, desktop computers, smartphones, tablets, etc. to consume multimedia content (video, TV, radio, etc.) delivered via the Internet, coping with variable Internet receiving conditions. Standardizing an adaptive streaming solution is meant to provide confidence to the market that the solution can be adopted for universal deployment, compared to similar but more proprietary solutions like Smooth Streaming by Microsoft, or HDS by Adobe.

Unlike, HLS, HDS and Smooth Streaming, DASH is codec-agnostic, which means it can use content encoded with any coding format like H.265, H.264, VP9 etc.

Standardization

MPEG-DASH technology was developed under MPEG. Work on DASH started in 2010; it became a Draft International Standard in January 2011, and an International Standard in November 2011. The MPEG-DASH standard was published as ISO/IEC 23009-1:2012 in April, 2012.

DASH is a technology related to Adobe Systems HTTP Dynamic Streaming, Apple Inc. HTTP Live Streaming (HLS) and Microsoft Smooth Streaming. DASH is based on Adaptive HTTP streaming (AHS) in 3GPP Release 9 and on HTTP Adaptive Streaming (HAS) in Open IPTV Forum Release 2. As part of their collaboration with MPEG, 3GPP Release 10 has adopted DASH (with specific codecs and operating modes) for use over wireless networks.

The DASH Industry Forum (DASH-IF) further promotes and catalyzes the adoption of MPEG-DASH and helps transition it from a specification into a real business. It consists of major streaming and media companies, including Microsoft, Netflix, Google, Ericsson, Samsung, Adobe, etc. and creates guidelines on the usage of DASH for different use cases in practice.

MPEG-DASH is integrated in other standards, e.g. MPEG-DASH is supported in HbbTV (as of Version 1.5).

Overview

DASH is an adaptive bitrate streaming technology where a multimedia file is partitioned into one or more segments and delivered to a client using HTTP. A media presentation description (MPD) describes segment information (timing, URL, media characteristics like video resolution and bit rates), and can be organized in different ways such as SegmentList, SegmentTemplate, SegmentBase and SegmentTimeline, depending on the use case. Segments can contain any media data, however the specification provides specific guidance and formats for use with two types of containers: ISO base media file format (e.g. MP4 file format) or MPEG-2 Transport Stream.

DASH is audio/video codec agnostic. One or more representations (i.e., versions at different resolutions or bit rates) of multimedia files are typically available, and selection can be made based on network conditions, device capabilities and user preferences, enabling adaptive bitrate streaming and QoE (Quality of Experience) fairness. DASH is also agnostic to the underlying application layer protocol. Thus, DASH can be used with any protocol, e.g., DASH over CCN.

On July 27, 2015, MPEG LA announced a call for MPEG-DASH-related patents in order to create a single patent pool for this technology.

Implementations

MPEG-DASH is available natively on Android through the ExoPlayer, on Samsung Smart TVs 2012+, LG Smart TV 2012+, Sony TV 2012+, Philips NetTV 4.1+, Panasonic Viera 2013+ and Chromecast. YouTube as well as Netflix already support MPEG-DASH, and different MPEG-DASH players are available.

While MPEG-DASH isn't directly supported in HTML5, there are JavaScript implementations of MPEG-DASH which allow using MPEG-DASH in web browsers using the HTML5 Media Source Extensions (MSE). There are also JavaScript implementations such as the bitdash player which support DRM for MPEG-DASH using the HTML5 Encrypted Media Extensions. In combination with WebGL, the HTML5-based adaptive bitrate streaming of MPEG-DASH enables also the efficient streaming of 360° video for live and on-demand use cases.

Clients and libraries

  • Dash.js is the official Dash Industry Forums Reference and Production player.
  • Shaka is the open source dash player from Google.
  • VLC Media Player 3.0 will ship a new client plugin for MP4/MPEG and Live streams.
  • The cross-platform FOSS multimedia framework GStreamer has supported MPEG-DASH and WebM DASH since at least v1.4.
  • The open-source library libdash is platform independent and runs on mobile platforms such as Android, iOS, Windows Phone.
  • bitmovin provides the bitdash MPEG-DASH player for HTML5 and Flash.
  • THEOplayer is currently looking for parties to test their MPEG-DASH video player.
  • Viblast Player has support for MPEG-DASH in HTML5 and provides an SDK for iOS and Android.
  • OSMO4 from GPAC at Telecom ParisTech supports MPEG-DASH.
  • DASH-JS from ITEC at University of Klagenfurt supports MPEG-DASH.
  • Radiant Media Player supports MPEG-DASH (DASH264 and WebM DASH) in HTML5.
  • Videogular is a video application framework for desktop and mobile powered by AngularJS, The HTML5 video player for AngularJS
  • libndash is an open source (Apache License) C++ library that provides all the functionality needed to build a full-featured native-code MPEG-DASH media player (not including decoding/rendering frames to a display).

Servers

Note that no specific support is required from the server for DASH content, with the exception of Live Streaming.

Services

Content Generators

  • ITEC's DASHEncoder.
  • MP4Box and its multimedia framework from GPAC at Telecom ParisTech
  • dashcast from Telecom ParisTech supports MPEG-DASH live streaming
  • MediaGoom MPEG-DASH Packager
  • Bento4 opensource tools and SDK

Other

  • ITEC offers a validation service for MPEG-DASH Media Presentation Description (MPD) files
  • Multiple DASH datasets are offered by the Institute of Information Technology (ITEC) at Alpen-Adria University Klagenfurt, the GPAC group at Telecom ParisTech and Digital TV Labs.
  • The BBC has DASH test streams, including DASH over HTTP/2.

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