Dynamic adaptive streaming over HTTP (DASH) is a suite of standards providing a standard solution for the efficient and easy streaming of multimedia using existing available HTTP infrastructure (particularly servers and CDNs, but also proxies, caches, etc.). DASH was motivated by the popularity of HTTP streaming and the existence of different protocols used in different streaming platforms, e.g. different manifest and segment formats.
By developing the DASH standard for HTTP streaming of multimedia content, MPEG has enabled a standard-based client to stream content from any standard-based server, thereby enabling interoperability between servers and clients of different vendors.
As depicted in Figure 59, the multimedia content is stored on an HTTP server in two components: 1) Media Presentation Description (MPD) which describes a manifest of the available content, its various alternatives, their URL addresses and other characteristics, and 2) Segments which contain the actual multimedia bitstreams in form of chunks, in single or multiple files.
Figure 59 – DASH model
Currently DASH is composed of 8 parts
- Part 1 – Media presentation description and segment formats specifies 1) the Media Presentation Description (MPD) which provides sufficient information for a DASH client to adaptive stream the content by downloading the media segments from a HTTP server, and 2) the segment formats which specify the formats of the entity body of the request response when issuing a HTTP GET request or a partial HTTP GET.
- Part 2 – Conformance and reference software the regular component of an MPEG standard
- Part 3 – Implementation guidelines provides guidance to implementors
- Part 4 – Segment encryption and authentication specifies encryption and authentication of DASH segments
- Part 5 – Server and Network Assisted DASH specifies asynchronous network-to-client and network-to-network communication of quality-related assisting information
- Part 6 – DASH with Server Push and WebSockets specified the carriage of MPEG-DASH media presentations over full duplex HTTP-compatible protocols, particularly HTTP/2 and WebSockets
- Part 7 – Delivery of CMAF content with DASH specifies how the content specified by the Common Media Application Format can be carried by DASH
- Part 8 – Session based DASH operation will specify a method for MPD to manage DASH sessions for the server to instruct the client about some operation continuously applied during the session.
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