"MPEG-DASH 标准2022新版发布：动态自适应流媒体传输技术详解"

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ISO_IEC 23009-1_2022是最新发布的MPEG-DASH标准，它是一项信息技术标准，涉及到动态自适应流媒体传输技术。具体来说，该标准涵盖了媒体呈现描述和片段格式两个方面。ISO/IEC 23009-1:2022标准第五版于2022年8月发布。该标准主要针对基于HTTP的动态自适应流媒体传输技术，即DASH。DASH技术允许视频和音频内容根据网络条件和终端设备的能力进行动态调整，以提供最佳的流媒体观看体验。ISO_IEC 23009-1_2022标准旨在规范DASH系统中的媒体呈现描述和片段格式，以确保各种终端设备和网络环境之间的互操作性。 ISO_IEC 23009-1_2022标准定义了一种用于描述DASH媒体表示和传输的通用语言，即媒体呈现描述。媒体呈现描述提供了有关媒体内容、媒体表示和相应的时序安排的信息。它描述了描述媒体呈现和传输的组件、媒体表示的参数、媒体时序相关信息等。通过使用统一的媒体呈现描述，DASH系统可以更好地适应各种终端设备和网络限制。此外，ISO_IEC 23009-1_2022标准还规定了用于DASH媒体片段传输的片段格式。片段格式描述了每个媒体片段的结构和编码方式，以及片段之间的关系和时序。片段格式的定义确保了在DASH系统中，不同媒体片段之间的平滑过渡和无缝切换。 ISO_IEC 23009-1_2022标准的发布对于推动DASH技术的应用和发展具有重要意义。该标准提供了一个统一的规范，使得不同厂商和服务提供商可以使用相同的标准实现和交互。通过遵循ISO_IEC 23009-1_2022标准，DASH技术可以更好地适应不同终端设备和网络环境，并提供更高质量的流媒体体验。总之，ISO_IEC 23009-1_2022是最新的MPEG-DASH标准，涵盖了媒体呈现描述和片段格式两个方面。该标准为DASH技术提供了统一的规范，促进了该技术在各种终端设备和网络环境中的应用和发展。通过遵循该标准，可以实现更好的流媒体传输效果和用户体验。

ISO/IEC 23009-1:2022(E)

GOP

group of pictures

GPS

global positioning system

HDCP

high-bandwidth digital content protection

HDMI

high definition multimedia interface

HEVC

high efficiency video coding

HTML

hypertext markup language

HTTP

hypertext transfer protocol

HTTPS

secure hypertext transfer protocol

IAB

interactive advertising bureau

IDR

instantaneous decoding refresh

internet protocol

ISO BMFF

ISO base media file format

LAT

Latest Arrival Time

MBT

minimum buffer time

MIME

multipurpose internet mail extensions

MPD

media presentation description

MPP

MPD patch

MVC

multi-view video coding

NGA

next generation audio

NTP

network time protocol

OATC

open authentication technical committee

OAuth

open standard for authorization

OMAP

online multimedia authorization protocol

PAT

program association table

PCR

program clock reference

PES

packetized elementary stream

PID

packet identifier

PMT

program map table

PSI

program specific information

PTS

presentation time stamp

RAP

random access point

SAML

security assertion markup language

SAP

stream access point

SEI

supplementary enhancement information

SNTP

simple NTP

SPS

sequence parameter set

ISO/IEC 23009-1:2022(E)

SRD

spatial relationship description

SVC

scalable video coding

TCP

transmission control protocol

TLS

transport layer security

transport stream

URI

uniform resource identifier

URL

uniform resource locator

URN

uniform resource name

UTC

coordinated universal time

UUID

universally unique identifier

VAST

video ad serving template

VOD

video-on-demand

XML

extensible mark-up language

3.3 Conventions

The following naming conventions apply in this document.

— Elements in an XML document are identified by an upper-case first letter and in bold face as

Element. To express that an element Element1 is contained in another element Element2, the

following format is used: Element2.Element1. If an element's name consists of two or more

combined words, camel-casing is typically used, e.g. ImportantElement. Elements may be present

either exactly once, or the minimum and maximum occurrence is defined by <minOccurs> ...

<maxOccurs>.

— Attributes in an XML document are identified by a lower-case first letter as well as they are preceded

by an '@'-sign, e.g. @attribute. To point to a specific attribute @attribute contained in an

element Element, one may write Element@attribute. If an attribute's name consists of two or

more combined words, camel-casing is typically used after the first word, e.g.

@veryImportantAttribute. Attributes may have assigned a status in the XML as mandatory

(M), optional (O), optional with default value (OD) and conditionally mandatory (CM).

— Namespace qualification of elements and attributes is used as per XML standards, in the form of

namespace:Element or @namespace:attribute. The fully qualified namespace is provided in

the schema fragment associated with the declaration. External specifications extending the

namespace of DASH are expected to document the element name in the semantic table with an

extension namespace prefix.

— Variables defined in the context of this document are specifically highlighted with italics, e.g.

InternalVariable.

— Structures that are defined as part of the hierarchical data model are identified by an upper-case first

letter, e.g. Period, Adaptation Set, Representation, Segment, etc.

— The term "this clause" refers to the entire clause included within the same first heading number. The

term "this subclause" refers to all text contained in the subclause with the lowest hierarchy heading.

ISO/IEC 23009-1:2022(E)

— For improved interoperability, this document uses ABNF notation according to IETF RFC 5234 to

specify certain underdefined values of XML attributes and elements.

4 Overview

4.1 System description

Dynamic adaptive streaming over HTTP (DASH) specifies XML and binary formats that enable delivery

of continuous media content from standard HTTP servers to HTTP clients and enable caching of content

by standard HTTP caches.

This document primarily defines two formats:

— The Media Presentation Description (MPD) describes a Media Presentation, i.e. a bounded or

unbounded presentation of continuous media content. In particular, it defines formats to announce

resource identifiers for Segments and to provide the context for these identified resources within a

Media Presentation. These resource identifiers are HTTP-URLs possibly combined with a byte range,

or with a data URL.

— The Segment formats specify the formats of the entity body of the HTTP response to an HTTP GET

request or a partial HTTP GET with the indicated byte range using HTTP/1.1 as defined in

IETF RFC 7233 to a resource identified in the MPD. Segments typically contain efficiently coded

media data and metadata conforming to or at least closely aligned with common media formats.

The MPD provides sufficient information for a client to provide a streaming service to the user by

accessing the Segments through the protocol specified in the scheme of the defined resources. In the

context of this document, the assumed protocol is HTTP/1.1. Such a client is referred to as a DASH Client

in the remainder of this document. However, this document does not provide a normative specification

for such a client.

Figure 1 shows a possible deployment architecture in which the formats defined in this document may

be used. Boxes with solid lines indicate devices that are mentioned in this document as they host or

process the formats defined in this document whereas dashed boxes are conceptual or transparent. This

document deals with the definition of formats that are accessible on the interface to the DASH Client,

indicated by the solid lines. Any other formats or interfaces are outside the scope of this document. In the

considered deployment scenario, it is assumed that the DASH Client has access to an MPD. The MPD

provides sufficient information for the DASH Client to provide a streaming service to the user by

requesting Segments from an HTTP server and demultiplexing, decoding and rendering the included

media streams.

ISO/IEC 23009-1:2022(E)

Figure 1 — Example system for DASH formats

Although the formats are initially designed to be used in the above deployment scenario, their application

is obviously not restricted to this scenario. The particular aspect on "HTTP" in DASH is the usage of HTTP-

URLs in the MPD for the purpose to refer to Segments. The usage of HTTP-URLs enables unique location

information and it provides well-defined methods to access the resources, in particular HTTP GET and

HTTP partial GET.

4.2 DASH Client model

The design of the formats defined in this document is based on the informative client model as shown in

Figure 2. The figure illustrates the logical components of a conceptual DASH Client model and the relation

to other components in a media streaming application. In this figure, the DASH access engine receives the

Media Presentation Description (MPD), constructs and issues requests and receives Segments or parts of

Segments. The DASH Client may use metadata provided in the MPD for the selection of media components

by communication with the media streaming application. Such metadata may for example include codec

capability information, language codes, accessibility information and other information for the selection

of media components. In the context of this document, the output of the DASH access engine consists of

media in MPEG container formats (ISO/IEC 14496-12 ISO base media file format or ISO/IEC 13818-1

MPEG-2 Transport Stream), or parts thereof, together with timing information that maps the internal

timing of the continuous media to the timeline of the Media Presentation. In Annex F, guidance on

enabling the use of this document with other container formats is provided. In addition, the DASH access

engine may also receive and extract Events that are related to the media time. The events may be

processed in the DASH Client or may be forwarded to an event processing application in the execution

environment of the DASH Client.

ISO/IEC 23009-1:2022(E)

Figure 2 — DASH Client model

Furthermore, Annex K defines the Service Description to support and guide DASH Client operations.

4.3 DASH data model overview

DASH is intended to support a media-streaming model for delivery of continuous media content in which

control lies primarily with the client. Clients may request data using the HTTP protocol from standard

web servers that have no DASH-specific capabilities. Consequently, this document focuses not on client

or server procedures but on the data formats used to provide a DASH Media Presentation.

The collection of encoded and deliverable versions of continuous media content and the appropriate

description of these form a Media Presentation. Media content is composed of a single or multiple

contiguous media content periods in time. Content in different media content periods may be completely

independent or certain periods of a Media Presentation may belong to the same Asset, for example a

Media Presentation is a collection of main program composed of multiple periods, each assigned to the

same Asset, and interleaved with inserted advertisement periods. Each media content period is

composed of one or multiple media content components, for example audio components in various

languages, different video components providing different views of the same program, subtitles in

different languages, etc. Each media content component has an assigned media content component

type, for example audio or video. The same asset over multiple periods may be identified by a DASH

descriptor enabling DASH Clients to maintain the continuity across periods' boundaries. Furthermore,

sub-assets composing the same asset may also be identified using a similar method. For instance, if an

asset is composed of multiple video components, sub-assets enable selecting the previously selected

video component after an ad insertion.

Each media content component may have several encoded versions, referred to as media streams. Each

media stream inherits the properties of the media content, the media content period, the media content

component from which it was encoded and, in addition, it gets assigned the properties of the encoding

process such as sub-sampling, codec parameters, encoding bitrate, etc. This descriptive metadata is

relevant for static and dynamic selection of media content components and media streams.

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