ETSI EN 300 743 V1.2.1 (2002-10)

Digital Video Broadcasting (DVB); Subtitling systems

REN/JTC-DVB-126

Digitalna videoradiodifuzija (DVB) – Sistemi za podnaslove

General Information

• Status: Published
• Publication Date: 17-Oct-2002
• Technical Committee: BROADCAS - EBU/CENELEC/ETSI on Broadcasting
• Current Stage: 12 - Completion
• Due Date: 18-Oct-2002
• Completion Date: 18-Oct-2002
• Ref Project: SIST EN 300 743 V1.2.1:2005 - Digital Video Broadcasting (DVB); Subtitling systems

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 300 743 V1.2.1:2005
01-november-2005
Digitalna videoradiodifuzija (DVB) – Sistemi za podnaslove
Digital Video Broadcasting (DVB); Subtitling systems
Ta slovenski standard je istoveten z: EN 300 743 Version 1.2.1
ICS:
33.170 Televizijska in radijska Television and radio
difuzija broadcasting
SIST EN 300 743 V1.2.1:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 300 743 V1.2.1:2005

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SIST EN 300 743 V1.2.1:2005

ETSI EN 300 743 V1.2.1 (2002-10)
European Standard (Telecommunications series)


Digital Video Broadcasting (DVB);
Subtitling systems

European Broadcasting Union Union Européenne de Radio-Télévision
EBU·UER

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SIST EN 300 743 V1.2.1:2005
 2 ETSI EN 300 743 V1.2.1 (2002-10)



Reference
REN/JTC-DVB-126
Keywords
broadcasting, digital, DVB, TV, video
ETSI
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© European Telecommunications Standards Institute 2002.
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ETSI

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SIST EN 300 743 V1.2.1:2005
 3 ETSI EN 300 743 V1.2.1 (2002-10)
Contents
Intellectual Property Rights.5
Foreword.5
1 Scope.6
2 References.6
3 Definitions and abbreviations.6
3.1 Definitions.6
3.2 Abbreviations.8
4 Introduction to DVB subtitling system .9
4.1 Overview.9
4.2 Data hierarchy and terminology .11
4.3 Temporal hierarchy and terminology .13
5 Subtitle decoder model.13
5.1 Decoder temporal model.14
5.1.1 Service acquisition.14
5.1.2 Presentation Time Stamps (PTS).14
5.1.3 Page composition.15
5.1.4 Region composition.15
5.1.5 Points to note .15
5.2 Buffer memory model .16
5.2.1 Pixel buffer memory.16
5.2.2 Region memory.16
5.2.3 Composition buffer memory.16
5.3 Cumulative display construction .17
5.4 Decoder rendering bandwidth model .17
5.4.1 Page erasure.17
5.4.2 Region move or change in visibility .17
5.4.3 Region fill.17
5.4.4 CLUT modification.17
5.4.5 Graphic object decoding.18
5.4.6 Character object decoding .18
6 PES packet format.18
7 The PES packet data for subtitling.19
7.1 Syntax and semantics of the PES data field for subtitling.19
7.2 Syntax and semantics of the subtitling segment .19
7.2.1 Page composition segment.20
7.2.2 Region composition segment.21
7.2.3 CLUT definition segment.24
7.2.4 Object data segment.25
7.2.4.1 Pixel-data sub-block.27
7.2.4.2 Syntax and semantics of the pixel code strings.28
7.2.5 End of display set segment .30
8 Requirements for the subtitling data .31
8.1 Scope of Identifiers .31
8.2 Scope of dependencies .31
8.2.1 Composition page.31
8.2.2 Ancillary page.31
8.3 Order of delivery .31
8.3.1 PTS field.31
8.4 Positioning of regions and objects.32
8.4.1 Regions.32
8.4.2 Objects sharing a PTS.32
ETSI

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SIST EN 300 743 V1.2.1:2005
 4 ETSI EN 300 743 V1.2.1 (2002-10)
8.4.3 Objects added to a region.32
9 Translation to colour components .32
9.1 4- to 2-bit reduction.33
9.2 8- to 2-bit reduction.33
9.3 8- to 4-bit reduction.33
10 Default CLUTs and map-tables contents .34
10.1 256-entry CLUT default contents.34
10.2 16-entry CLUT default contents.35
10.3 4-entry CLUT default contents.35
10.4 2_to_4-bit_map-table default contents.36
10.5 2_to_8-bit_map-table default contents.36
10.6 4_to_8-bit_map-table default contents.37
11 Structure of the pixel code strings (informative).37
Annex A (informative): How the DVB subtitling system works.39
A.1 Data hierarchy and terminology .39
A.2 Temporal hierarchy and terminology .39
A.3 Decoder temporal model .39
A.4 Decoder display technology model .39
A.4.1 Region based with indexed colours.39
A.4.2 Colour quantization.40
A.5 Decoder rendering bandwidth model .40
A.6 Examples of the subtitling system in operation.40
A.6.1 Double buffering.40
A.6.1.1 Instant graphics.41
A.6.1.2 Stenographic subtitles.44
A.7 Glossary.46
Annex B (informative): Bibliography.47
History .48

ETSI

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SIST EN 300 743 V1.2.1:2005
 5 ETSI EN 300 743 V1.2.1 (2002-10)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://webapp.etsi.org/IPR/home.asp).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This European Standard (Telecommunications series) has been produced by Joint Technical Committee (JTC)
Broadcast of the European Broadcasting Union (EBU), Comité Européen de Normalisation ELECtrotechnique
(CENELEC) and the European Telecommunications Standards Institute (ETSI).
NOTE: The EBU/ETSI JTC Broadcast was established in 1990 to co-ordinate the drafting of standards in the
specific field of broadcasting and related fields. Since 1995 the JTC Broadcast became a tripartite body
by including in the Memorandum of Understanding also CENELEC, which is responsible for the
standardization of radio and television receivers. The EBU is a professional association of broadcasting
organizations whose work includes the co-ordination of its members' activities in the technical, legal,
programme-making and programme-exchange domains. The EBU has active members in about 60
countries in the European broadcasting area; its headquarters is in Geneva.
European Broadcasting Union
CH-1218 GRAND SACONNEX (Geneva)
Switzerland
Tel: [phone]
Fax: [phone]

Founded in September 1993, the DVB Project is a market-led consortium of public and private sector organizations in
the television industry. Its aim is to establish the framework for the introduction of MPEG-2 based digital television
services. Now comprising over 200 organizations from more than 25 countries around the world, DVB fosters
market-led systems, which meet the real needs, and economic circumstances, of the consumer electronics and the
broadcast industry.

National transposition dates
Date of adoption of this EN: 4 October 2002
Date of latest announcement of this EN (doa): 31 January 2003
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 31 July 2003
Date of withdrawal of any conflicting National Standard (dow): 31 July 2003

ETSI

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SIST EN 300 743 V1.2.1:2005
 6 ETSI EN 300 743 V1.2.1 (2002-10)
1 Scope
The present document specifies the method by which subtitles, logos and other graphical elements may be coded and
carried in DVB bitstreams. The system applies Colour Look-Up Tables (CLUTs) to define the colours of the graphical
elements. The transport of the coded graphical elements is based on the MPEG-2 system described in
ISO/IEC 13818-1 [1].
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
• References are either specific (identified by date of publication and/or edition number or version number) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies.
[1] ISO/IEC 13818-1: "Information technology - Generic coding of moving pictures and associated
audio information: Systems".
[2] ETSI EN 300 468: "Digital Video Broadcasting (DVB); Specification for Service Information (SI)
in DVB systems".
[3] ITU-R Recommendation BT.601: "Studio encoding parameters of digital television for standard
4:3 and wide-screen 16:9 aspect ratios".
[4] ITU-R Recommendation BT.656-4: "Interfaces for digital component video signals in 525-line
and 625-line television systems operating at the 4:2:2 level of Recommendation ITU-R BT.601
(Part A)".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
ancillary page: means of conveying subtitle elements that may be shared by multiple subtitle services within a subtitle
stream
NOTE: For example, an ancillary page can be used to carry logos or character glyphs.
Colour Look-Up Table (CLUT): look-up table applied in each region for translating the objects' pseudo-colours into
the correct colours to be displayed
CLUT-family: family of CLUTs which may consist of:
- one CLUT with 4 entries;
- one CLUT with 16 entries;
- one CLUT with 256 entries.
ETSI

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 7 ETSI EN 300 743 V1.2.1 (2002-10)
A CLUT-family is used in a region to define colours for decoders with different rendering capabilities.
NOTE: Three CLUTs are defined to allow flexibility in the decoder design. Not all decoders may support a
CLUT with 256 entries, some may provide sixteen or even only four entries. A palette of four colours
might be enough for graphics that are basically monochrome, like very simple subtitles, while a palette of
sixteen colours allows for cartoon-like coloured objects or coloured subtitles with antialiassed edges.
composition page: means of conveying subtitle elements for one specific subtitle service
display set: set of subtitle segments of a specific subtitle service to which the same PTS value is associated
epoch: period of time for which the decoder maintains an invariant memory layout
NOTE: This layout may be altered by resets to the decoder state caused by receiving page composition segments
with page state = "mode change". The end of an epoch therefore signals the "death" of a page. The epoch
may, if so desired, be considered to be the highest level data structure in DVB subtitling.
object: graphical unit that can be positioned within a region; examples of an object include a character glyph, a logo, a
map, etc.
NOTE: Each object has its own object_id.
Packet IDentifier (PID): Transport packet identifier
NOTE: See ISO/IEC 13818-1 [1].
page: Set of subtitles for a subtitle service during a certain period. A page consists of one or more page instances.
Each page update or refresh will result in a new page instance. A page contains a number of regions, and in each region
there may be a number of objects.
page composition: composition (use and positioning) of regions that may be displayed within the page
NOTE: At any new page instance the page composition may change; for example, some regions may not yet or
no longer be displayed. At any one time, only one page composition can be active for displaying.
page instance: period of time during which that page does not change i.e. there is no change to the page composition,
to any region composition, to any object within a region or any applicable CLUT
NOTE: Typically, a new page instance is defined by the PTS of a display set.
PES packet: See ISO/IEC 13818-1 [1].
pixel-data: string of data bytes that contains, in coded form, the representation of a graphical object
Presentation Time Stamp (PTS): See ISO/IEC 13818-1 [1].
region: rectangular area on the page in which objects can be positioned
NOTE: Regions may be shared by multiple subtitling services within the same subtitle stream. Objects that
share one or more horizontal scan lines on the screen are included in the same region.
region composition: composition (use and positioning) of objects within a region
subtitle element: subtitle data used within a page composition and contained within a subtitle segment
NOTE: Regions, region compositions, CLUTs and object data are examples of subtitle elements.
subtitle segment: basic syntactical element of a subtitle stream
subtitle service: service that provides subtitling for a program for a certain purpose, such as subtitles in a specific
language or for the hard of hearing
NOTE 1: A subtitle service is displayed as a series of one or more pages.
NOTE 2: Typically, a subtitle service meets a single communication requirement (e.g. the graphics to provide
subtitles in one language for one program).
ETSI

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 8 ETSI EN 300 743 V1.2.1 (2002-10)
subtitle stream: stream of subtitling segments carried in transport packets identified by the same PID
NOTE: A subtitle stream contains one or more subtitle services.
transport packet: See ISO/IEC 13818-1 [1].
transport stream: stream of transport packets carrying one or more MPEG programs
NOTE: See ISO/IEC 13818-1 [1].
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
bslbf bit string, left bit first
Cb Chrominance value
NOTE: As defined in ITU-R Recommendation BT.601 [3], clause 7.2.3.
CLUT Colour Look-Up Table
Cr Chrominance value
NOTE: As defined in ITU-R Recommendation BT.601 [3], see clause 7.2.3.
DVB Digital Video Broadcasting
IRD Integrated Receiver Decoder
MPEG Moving Pictures Experts Group (WG11 in SC 29 of JTC1 of ISO/IEC)
PCR Programme Clock Reference
PCS Page Composition Segment
PES Packetized Elementary Stream
NOTE: As defined in ISO/IEC 13818-1 [1].
PID Packet IDentifier
NOTE: As defined in ISO/IEC 13818-1 [1].
PID transport packet identifier
NOTE: As defined in ISO/IEC 13818-1 [1].
PMT Program Map Table
NOTE: As defined in ISO/IEC 13818-1 [1].
PTS Presentation Time Stamp
NOTE: As defined in ISO/IEC 13818-1 [1].
RCS Region Composition Segment
ROM Read-Only Memory
T Transparency value
TS Transport Stream
NOTE: As defined in ISO/IEC 13818-1 [1].
uimsbf unsigned integer, most significant bit first
Y luminance value
NOTE: As defined in ITU-R Recommendation BT.601 [3], see clause 7.2.3.
ETSI

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 9 ETSI EN 300 743 V1.2.1 (2002-10)
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.

Region 1

Shall we ?
Said the fly on the mirror.
Region 2


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

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 10 ETSI EN 300 743 V1.2.1 (2002-10)
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 sch
...