DVB字幕系统标准详解

需积分: 34 104 浏览量更新于2024-07-23 收藏 395KB PDF 举报

"Ets300743 dvb 字幕标准" 《ETSI EN 300743》是欧洲电信标准协会（ETSI）发布的一份关于数字视频广播（DVB）字幕系统的标准文档，版本为V1.3.1，发布于2006年11月。这份标准主要由欧洲广播联盟（EBU）和欧洲电信标准协会（ETSI）联合制定，旨在规范DVB系统中的字幕服务，确保数字电视内容的无障碍性，尤其是对听力障碍或非母语观众。该标准涵盖了以下几个关键知识点： 1. **字幕格式**：规定了字幕数据的编码、传输和解码方式，包括字幕的格式化、颜色、字体、位置和时间轴等信息，以确保在不同设备上的一致显示。 2. **字幕编码**：描述了如何将字幕内容编码为二进制数据，通常采用MPEG-2 Transport Stream（TS）或EnhancedAC-3（E-AC-3）等格式，以便在数字电视信号中嵌入。 3. **传输机制**：详细定义了字幕信息在DVB传输流中的位置和结构，使得接收端可以正确识别和解析字幕数据。 4. **兼容性**：标准确保字幕服务与各种接收设备（如数字电视、个人计算机、移动设备等）的兼容性，不论用户使用何种接收方式都能获取字幕。 5. **多语言支持**：DVB字幕系统支持多语言字幕，观众可以选择自己需要的语言，增强了内容的国际化。 6. **实时性和互动性**：标准也涉及实时字幕的处理，例如新闻或体育直播的即时翻译，以及互动电视中的字幕需求。 7. **错误检测与恢复**：在传输过程中可能出现的数据丢失或错误，标准提供了错误检测和恢复机制，保证字幕的完整性和可读性。 8. **书签功能**：提到的“有书签的哦，亲！”可能是指文档中包含便于查阅和导航的书签，方便读者快速定位到特定内容。 9. **版本管理和更新**：由于技术的不断发展，标准可能会有新的修订或状态变化，用户应关注ETSI官网获取最新版本，确保遵循的是最新的规范。《ETSI EN 300743》是DVB字幕系统的核心标准，它确保了字幕在数字广播领域的标准化和高质量，促进了信息的无障碍传播。对于DVB相关的开发、设计和维护人员来说，理解并遵循这一标准至关重要。

ETSI

TSI EN 300 743 V1.3.1 (2006

uimsbf unsigned integer, most significant bit first

Y luminance value

NOTE: As defined in ITU-R Recommendation BT.601 [3], clause 7.2.3.

4 Introduction to DVB subtitling system

The present document specifies the DVB subtitling system for the transport and coding of subtitles.

4.1 Overview

The DVB subtitling system defined in the present document provides a syntax for decoding subtitle streams. A subtitle

stream conveys one or more subtitle services; each service containing the textual and/or graphical information needed

to provide subtitles or glyphs for a particular purpose. Separate subtitle services may be used, for example, to convey

subtitles in several languages.

Each subtitle service displays its information in a sequence of so-called pages that are intended to be overlayed on the

associated video image. A subtitle page contains one or more regions, each region being a rectangular area with a

specified set of attributes. These attributes include a region identifier, the horizontal and vertical size, pixel depth and

background colour. A region is used as the background structure into which graphical objects are placed. An object

may represent a character, a word, a line of text or an entire sentence; it might also define a logo or icon.

The use and positioning of objects within a region is defined by the region composition segment.

The use and positioning of regions within a page is defined by the page composition segment, in which a list of

displayed regions is provided, each with their own spatial position. A page composition need not change when objects

are added to or removed from a region. Furthermore regions may be declared but not used. By way of example one

region can be used to display multiple subtitle fragments, as depicted in figure 1. First the text "Shall we?" is displayed

in the region; subsequently this text is removed and the new text "Said the fly on the mirror" is displayed. It is possible

to use more than one region at the same time; for example one region could be used to display subtitles on the bottom of

the screen, while another one might be used to display a logo somewhere else on the screen.

Shall we ?

Said the fly on the mirror.

➐ ➐

Region 1

Region 2

Figure 1: Two regions overlayed on top of video; one with a logo and another one with subtitles.

Note that the subtitles are positioned within the same region.

A DVB subtitle stream is carried in PES packets and the timing of their presentation is defined by the PTS in the PES

header. Upon reception and decoding of the subtitle data for a page (such as the page composition, the region

composition, the objects to be used and any other associated data) the page contents are displayed at the time indicated

by the associated PTS. When objects are to be added, the decoder receives region composition updates and the data for

the new objects, and will display the updated page at the time indicated by the new PTS. At the page update only page

differences need be provided. To improve random access to DVB subtitling, a page refresh is also possible. At page

refresh all the subtitling data needed to display a page is provided. Each page update or refresh will result in a new page

instance. A page ceases to exist after the time-out of the page, or when a new page is defined.

ETSI

TSI EN 300 743 V1.3.1 (2006

To provide efficient use of display memory in the decoder the DVB subtitling system uses region based graphics with

indexed pixel colours. Pixel depths of 2, 4 and 8 bits are supported allowing up to 4, 16 or 256 different pixel codes to

be used in each region. Each region is associated with a single CLUT family to define the colour and transparency for

each of the pixel codes. In most cases, one CLUT is sufficient to present correctly the colours of all objects in a region,

but if it is not enough, the objects can be split horizontally into smaller objects across separate vertically adjacent

regions with one CLUT each.

The use of CLUTs allows colour schemes to be dynamic. The colours that correspond to the entries within the region

can be redefined at any suitable time, for instance in case of a CLUT with four entries from a black-grey-white scheme

to a blue-grey-yellow scheme. Furthermore, a graphical unit may be divided into several regions each using a different

CLUT, i.e. a different colour scheme may be applied in each of the regions. At the discretion of the encoder, objects

designed for displays supporting 16 or 256 colours can be decoded into displays supporting fewer colours. A

quantization algorithm is defined to ensure that the result of this process can be predicted by the originator. Use of this

feature allows a single data stream to be decoded by a population of decoders with mixed, and possibly evolving,

capabilities.

A subtitle stream may transport multiple subtitle service components. In this case the pages of one particular subtitle

service are all identified by the same page-id value. This value is used when transporting the subtitling data so as to

provide a mechanism to retrieve the data that is specific to a service from a subtitle stream. The subtitling system allows

sharing of subtitling data between services within the same subtitle stream. A frequent and often preferred method is to

convey the distinct services in different streams on separate PIDs. In either case the appropriate PID, language and

page-ids will be signalled in the Program Map Table (PMT) for the television service of interest (language and page-id

in the subtitling descriptor defined in DVB-SI [2]). These two approaches are illustrated in figure 2.

ubtitle data signalled

by page-id = 1

(spanish)

ubtitle data signalled

by page-id = 2

(italian)

Subtitle data signalled

by page-id = 3

(shared)

PES packet data

language = spanish

omposition

ge_id = 1

ancillary-page _id = 3

language = italian

composition-page_id = 2

ancillary-page_id = 3

Subtitle descriptors

ssociated with this

ubtitle stream in the

….

PID = X

PMT

a: Example of use of different page_ids to distinguish between different subtitle languages

for the same service (shown with a shared ancillary page)

ETSI

TSI EN 300 743 V1.3.1 (200

language = spanish

composition-page_id = 1

ancillary-page_id = 1

language = italian

composition-page_id = 1

ancillary-page_id = 1

Subtitle descriptors

associated with these

subtitle streams in the

….

PID = X

Subtitle data signalled

by page_id = 1

(

spanish)

PES packet data

PID = X

PMT

PID=Y

PES packet data

PID = Y

Subtitle data

signalled by page_id = 1

(italian)

b: Example of use of PIDs to distinguish between different subtitle languages

for the same service (shown with no ancillary page)

Figure 2: Example of two ways of conveying dual language subtitles (one using shared data)

In summary, the DVB subtitling system provides a number of techniques that allow efficient transmission of the

subtitling data:

• objects that occur more than once within a region need only be transmitted once, and then positioned multiple

times within the region;

• objects used in more than one subtitle service need only be transmitted once;

• pixel data within objects are compressed using run-length coding;

• where the gamut of colours required for part of a graphical object is suitably limited, that part can be coded

using a smaller number of bits per pixel and a map table. For example, an 8-bit per pixel graphical object may

contain areas coded as 4 or 2-bits per pixel each preceded by a map table to map the 16 or 4 colours used onto

the 256 colour set of the region. Similarly, a 4-bit per pixel object may contain areas coded as 2-bits per pixel;

• colour definitions can be coded using either 16 or 32-bits per CLUT entry. This provides a trade-off between

colour accuracy and transmission bandwidth;

• only those CLUT values to be used need be transmitted.

The above features are fully supported within the DVB subtitling system.

Subtitle streams intended for HDTV may include an optional data structure called the display_definition_segment

which explicitly defines the display size for which that stream has been created.

Subtitle streams associated with standard definition TV services need not include a display_definition_segment and

may be encoded in accordance with EN 300 743 (V1.2.1) [5]. Such streams will be nevertheless be decodable by

decoders compliant with this and any later versions of EN 300 743 [5].

Subtitle streams associated with standard definition TV services and intended to be decoded by decoders designed to

EN 300 743 (V1.2.1) [5] shall not include a display_definition_segment.

In addition, functionality is provided to allow more efficient operation where there are private agreements between the

data provider and the manufacturer of the decoder:

• objects resident in ROM in the decoder can be referenced;

剩余50页未读，继续阅读

赛斯迪恩

粉丝: 2
资源: 6

DVB字幕系统标准详解

ETSI EN 300 743 (1997-9).pdf

EN300 743

数字电视字幕解码设计方法浅析

DVB标准下数字机顶盒字幕解码与显示系统设计详解

DVB数字视频广播字幕系统详解：段落结构与标准介绍

DVB数字字幕机：设计、实现与扩展研究

DVB数字电视字幕解码显示系统设计与实现

DVB标准详解与TS流解析

深入解析DVB SI与EPG技术

基于python的垃圾分类系统资料齐全+详细文档.zip

最新资源