SIST EN 303 560 V1.1.1:2018

EUROPEAN STANDARD
Digital Video Broadcasting (DVB);
TTML subtitling systems
2 ETSI EN 303 560 V1.1.1 (2018-05)

Reference
DEN/JTC-DVB-375
Keywords
broadcast, digital, DVB, subtitle, TV

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ETSI
3 ETSI EN 303 560 V1.1.1 (2018-05)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 6
Introduction . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 8
3 Definitions and abbreviations . 9
3.1 Definitions . 9
3.2 Abbreviations . 10
4 Default DVB TTML subtitle conformance point . 11
4.1 Introduction . 11
4.2 Document Constraints . 11
4.2.1 General . 11
4.2.2 Regions . 12
4.2.3 Document complexity . 12
4.2.4 Document encoding . 12
4.2.5 Namespaces . 12
4.2.6 Guidance for document authors and content providers (informative) . 12
4.2.6.1 Overview . 12
4.2.6.2 Font mapping for generic font family names . 12
4.2.6.3 Default text colour. 13
4.2.6.4 Requirement for support of optional features . 13
4.2.6.5 Specifying active area . 13
5 Delivery . 13
5.1 IP delivery . 13
5.2 Broadcast TS delivery . 13
5.2.1 PSI/SI signalling . 13
5.2.1.1 TTML subtitling descriptor . 13
5.2.1.2 Example TTML profile signalling . 17
5.2.1.2.1 Signalling conformance only to the default conformance point . 17
5.2.1.2.2 Signalling conformance to only EBU-TT-D . 17
5.2.1.2.3 Signalling conformance with EBU-TT-D and the default conformance point . 17
5.2.1.2.4 Signalling conformance to only IMSC1 Text Profile . 18
5.2.1.3 Presentation properties in qualifier field . 18
5.2.1.4 Component descriptors for TTML subtitles . 19
5.2.2 TS packetization . 19
5.2.2.1 PES packet format and carriage in the TS . 19
5.2.2.2 PES packet payload format for TTML subtitling . 20
5.2.2.2.1 General PES payload field syntax and segment types . 20
5.2.2.2.2 Occurrences of segments in one PES packet . 21
5.2.2.2.3 Uncompressed TTML document subtitle segment . 21
5.2.2.2.4 gzip compressed TTML document subtitle segment . 21
5.2.3 TTML segmentation . 21
5.2.3.1 General . 21
5.2.3.2 Concept of ISDs . 22
5.2.3.3 Active Period of a TTML segment . 22
5.2.3.4 TTML documents segmentation rules . 22
5.2.3.5 Subtitle stream in the absence of subtit les . 22
5.2.3.6 Continuation of a subtitle across adjacent segments . 22
5.2.3.7 Untimed elements in TTML segments . 23
5.2.3.8 Examples of TTML segmentation . 23
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4 ETSI EN 303 560 V1.1.1 (2018-05)
5.2.4 Synchronization . 23
5.2.4.1 Relationship between MPEG system clock and TTML timeline . 23
5.2.4.2 Failure of TTML segment reception . 24
5.2.4.3 Synchronization examples . 24
5.2.5 Acquisition time . 27
5.3 Font download . 27
5.3.1 Introduction. 27
5.3.2 Font delivery signalling mechanism . 28
5.3.2.1 Overview . 28
5.3.2.2 Linkage descriptor with linkage type 0x20 . 29
5.3.2.2.1 Introduction . 29
5.3.2.2.2 Linkage descriptor with linkage type 0x20 structure . 29
5.3.2.2.3 Linkage descriptor with linkage type 0x20 location, occurrence and prioritization . 30
5.3.2.3 Downloadable Font Information Table (DFIT) . 30
5.3.2.3.1 DFIT structure . 30
5.3.2.3.2 font_info_type in the loop of the DFIS . 32
5.3.3 IP download fonts . 33
5.3.4 Broadcast download fonts . 33
5.3.5 Downloaded font file, font name and font-id association . 33
6 IRD requirements . . 34
6.1 General support . 34
6.2 Forward compatibility . 34
6.3 Support of PSI/SI signalling and subtitle service selection . 34
6.3.1 PSI/SI signalling . 34
6.3.2 Determining which subtitle services can be rendered . 34
6.3.3 Subtitle service selection . 34
6.4 Font support in IRDs . 35
6.4.1 Supported fonts and font family name mapping . 35
6.4.2 Downloadable font retrieval . 35
6.4.3 Font selection for subtitle rendering . 36
6.5 Rendering requirements . 36
6.5.1 Playback free-running when A/V sync lost temporarily . 36
6.5.2 Behaviour during trick play . 36
6.5.3 Subtitle composition with HDR video . 36
6.5.4 Cropping and scaling of video . 37
6.6 Additional TTML processor requirements . 37
Annex A (informative): Change History . 38
History . 39

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5 ETSI EN 303 560 V1.1.1 (2018-05)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables 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 (https://ipr.etsi.org/).
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.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This European Standard (EN) 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: +41 22 717 21 11
Fax: +41 22 717 24 81
The Digital Video Broadcasting Project (DVB) is an industry-led consortium of broadcasters, manufacturers, network
operators, software developers, regulatory bodies, content owners and others committed to designing global standards
for the delivery of digital television and data services. DVB fosters market driven solutions that meet the needs and
economic circumstances of broadcast industry stakeholders and consumers. DVB standards cover all aspects of digital
television from transmission through interfacing, conditional access and interactivity for digital video, audio and data.
The consortium came together in 1993 to provide global standardization, interoperability and future proof
specifications.
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6 ETSI EN 303 560 V1.1.1 (2018-05)
National transposition dates
Date of adoption of this EN: 30 April 2018
Date of latest announcement of this EN (doa): 31 July 2018
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 31 January 2019
Date of withdrawal of any conflicting National Standard (dow): 31 January 2019

Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
Today's broadcast content can be distributed in many forms and via many different paths. Whilst broadcast services
traditionally relied on bitmap-based subtitles because of processing simplicity, advanced processing and text rendering
have made text-based approaches feasible. These offer more flexibility and better options to improve the user
experience. TTML (Timed Text Markup Language) is established as a common solution for IP-based platforms, but
multiple profiles exist.
In Europe, the EBU Group 'Subtitles in XML' published the EBU-TT-D TTML profile [20] which was adopted by the ®
DVB DASH specification as defined in ETSI TS 103 285 [6] and by HbbTV as defined in ETSI TS 102 79 [5]. The
W3C later published the IMSC1 TTML profiles [4], which were adopted by ATSC.
There are only minor differences between EBU-TT-D [3], [20] and IMSC1 Text Profile.
The present specification builds on the existing widespread device support for EBU-TT-D [20], in particular through ®
support for HbbTV , to enable the distribution of TTML subtitles together with audio/video content via broadcast.
Clause 4 specifies TTML subtitle constraints for a default conformance point, to be supported by both EBU-TT-D [3],
[20] and IMSC1 Text Profile compatible processors.
Clause 5 specifies subtitle delivery, including PSI/SI signalling, TS packetisation, TTML segmentation and
synchronization requirements.
Finally clause 6 specifies IRD requirements.

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7 ETSI EN 303 560 V1.1.1 (2018-05)
1 Scope
The present document specifies the transport of TTML [2] subtitle streams in DVB MPEG-2 transport streams,
based on the MPEG-2 system described in ISO/IEC 13818-1 [1]. TTML is an XML-based representation. The present
document provides syntax for delivery of TTML subtitle streams over MPEG-2 transport stream, and is based on
EBU-TT-D [3] compatible with the IMSC1 [4] Text Profile of W3C TTML [2].
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference/.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ISO/IEC 13818-1: "Information technology -- Generic coding of moving pictures and associated
audio information -- Part 1: Systems".
[2] W3C Recommendation (TTML): "Timed Text Markup Language 1 (TTML1) (Second Edition)".
NOTE: Available at http://www.w3.org/TR/2013/REC-ttml1-20130924/.
[3] EBU Tech 3380 "EBU-TT-D Subtitling Distribution Format", version 1.0.1.
NOTE: Available at https://tech.ebu.ch/publications/tech3380.
[4] W3C Recommendation (IMSC1): "TTML Profiles for Internet Media Subtitles and Captions 1.0.1
(IMSC1)".
NOTE: Available at http://www.w3.org/TR/ttml-imsc1.0.1/.
[5] ETSI TS 102 796: "Hybrid Broadcast Broadband TV".
[6] ETSI TS 103 285: "Digital Video Broadcasting (DVB); MPEG-DASH Profile for Transport of
ISO BMFF Based DVB Services over IP Based Networks".
[7] DVB BlueBook A038: "Digital Video Broadcasting (DVB); Specification for Service Information
(SI) in DVB systems".
NOTE: Available at http://www.dvb.org/resources/public/standards/a038_dvb_spec_december_2017.pdf.
[8] ISO 639-2: "Codes for the representation of names of languages -- Part 2: Alpha-3 code".
[9] ISO/IEC 8859-1: "Information technology -- 8-bit single-byte coded graphic character sets --
Part 1: Latin alphabet No. 1".
[10] W3C Working Group Note: "TTML Media Type Definition and Profile Registry".
NOTE: Available at http://www.w3.org/TR/ttml-profile-registry/.
[11] ETSI EN 301 192: "Digital Video Broadcasting (DVB); DVB specification for data broadcasting".
[12] ETSI TS 102 809: "Digital Video Broadcasting (DVB); Signalling and carriage of interactive
applications and services in hybrid broadcast/broadband environments".
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8 ETSI EN 303 560 V1.1.1 (2018-05)
[13] ETSI TS 102 851: "Digital Video Broadcasting (DVB); Uniform Resource Identifiers (URI) for
DVB Systems".
[14] IETF RFC 1952: "GZIP file format specification version 4.3".
[15] DVB BlueBook A126: "Digital Video Broadcasting (DVB); Allocation of identifiers and codes for
Digital Video Broadcasting (DVB) systems".
NOTE: Available at https://www.dvb.org/resources/public/standards/a126_allocation_identifiers.pdf.
[16] W3C Recommendation (XML): "Extensible Markup Language (XML) 1.0 (Fifth Edition)".
NOTE: Available at https://www.w3.org/TR/2008/REC-xml-20081126/.
[17] EBU Tech 3381: "Carriage of EBU-TT-D in ISOBMFF", version 1.0.
NOTE: Available at https://tech.ebu.ch/publications/tech3381.
[18] W3C Recommendation 13 December 2012 (WOFF): "Web Open Font Format (WOFF) 1.0".
NOTE: Available at http://www.w3.org/TR/2012/REC-WOFF-20121213/.
[19] ISO/IEC 14496-22:2015: "Information technology -- Coding of audio-visual objects --
Part 22: Open Font Format".
[20] EBU Tech 3380: "EBU-TT-D Subtitling Distribution Format", version 1.0.
NOTE: Available at https://tech.ebu.ch/publications/tech3380.
[21] IETF RFC 3986: "Uniform Resource Identifier (URI): Generic Syntax".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] W3C Recommendation (WCAG): "Web Content Accessibility Guidelines (WCAG) 2.0".
NOTE: Available at https://www.w3.org/TR/2008/REC-WCAG20-20081211/.
[i.2] W3C Candidate Recommendation (CSS): "CSS Fonts Module Level 3: Font matching algorithm".
NOTE: Available at https://www.w3.org/TR/css-fonts-3/#font-matching-algorithm.
[i.3] IEC 61966-2-1:1999: "Multimedia systems and equipment - Colour measurement and
management - Part 2-1: Colour management - Default RGB colour space - sRGB".
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9 ETSI EN 303 560 V1.1.1 (2018-05)
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
Intermediate Synchronic Document (ISD): temporally bounded (possibly empty) subset of TTML content during
which no elements change state between active and inactive
NOTE: A TTML document can conceptually be considered as a contiguous sequence of ISDs.
maximum period of activation (MPA): maximum duration a single TTML segment can be active, referred to as T
MPA
Packet IDentifier (PID): transport stream packet identifier
NOTE: See ISO/IEC 13818-1 [1].
PES packet: See ISO/IEC 13818-1 [1].
Presentation Time Stamp (PTS): See ISO/IEC 13818-1 [1].
reserved_zero_future_use: when used in the clause defining the coded bit stream, indicates that the value may be used
in the future for ETSI defined extensions
NOTE: All "reserved_zero_future_use" bits are set to "0".
subtitle segment: basic syntactical element of a subtitle stream
NOTE: The present document is structured to allow other types of subtitle segments to be defined in the future. In
this version of the specification, all subtitle segments are TTML segments.
subtitle service properties: properties defined by TTML subtitling descriptor which include but are not limited to
language, purpose, TTS_suitability, font usage, and qualifier
subtitle service: service that provides subtitling for an MPEG program (DVB service) with a set of subtitle service
properties
subtitle service qualifier variants: set of subtitle services whose subtitle service properties are identical except for
the qualifier_present_flag and qualifier fields in the TTML subtitling descriptor
subtitle stream: stream of subtitle segments carried in transport stream packets identified by the same PID,
containing a single subtitle service
transport stream packet: See ISO/IEC 13818-1 [1].
transport stream: stream of transport stream packets carrying one or more MPEG programs
NOTE: See ISO/IEC 13818-1 [1].
TTML document chunk: self-contained and temporally bounded subset of a TTML document [2]
NOTE: Self-contained in this context means that the document chunk contains all elements to render this subset
except the actual fonts used.
TTML segment: subtitle segment whose payload is an XML serialization of a TTML document chunk, concretely
encoded as a well-formed XML 1.0 [16] document
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10 ETSI EN 303 560 V1.1.1 (2018-05)
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ATSC Advanced Television Systems Committee
BAT Bouquet Association Table
bslbf bit string, left bit first
NOTE: The rightmost bit of a bslbf field is always referred to as b . This will be the last bit of the field
transmitted.
CRC Cyclic Redundancy Check
CSS Cascading Style Sheets
DASH Dynamic Adaptive Streaming over HTTP
DFIS Downloadable Font Information Section
DFIST Downloadable Font Information sub_table
DFIT Downloadable Font Information Table
DSI Download Server Initiate
DSM-CC Digital Storage Media - Command and Control
DVB Digital Video Broadcasting
DVB URI Uniform Resource Identifiers for DVB systems
NOTE: As defined in ETSI TS 102 851 [13].
EIT Event Information Table
NOTE: As defined in DVB BlueBook A038 [7]. ®
HbbTV Hybrid broadcast broadband TV
NOTE: As defined in ETSI TS 102 796 [5].
HDR High Dynamic Range
HRM Hypothetical Render Model
HTTP Hypertext Transfer Protocol
HTTPS Hypertext Transfer Protocol - Secure
IP Internet Protocol
IRD Integrated Receiver Decoder
ISD Intermediate Synchronic Document
MPA Maximum Period of Activation
MPEG Moving Pictures Experts Group
NIT Network Information Table
NOTE: As defined in ISO/IEC 13818-1 [1].
PES Packetized Elementary Stream
NOTE: As defined in ISO/IEC 13818-1 [1].
PID transport stream Packet IDentifier
NOTE: As defined in ISO/IEC 13818-1 [1].
PMT Program Map Table
NOTE: As defined in ISO/IEC 13818-1 [1].
PSI Program Specific Information
PTS Presentation Time Stamp
NOTE: As defined in ISO/IEC 13818-1 [1].
RGB Red Green Blue
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11 ETSI EN 303 560 V1.1.1 (2018-05)
SDT Service Description Table
NOTE: As defined in DVB BlueBook A038 [7].
SI Service Information
NOTE: As defined in ISO/IEC 13818-1 [1].
sRGB standard Red Green Blue
NOTE: As defined in IEC as IEC 61966-2-1:1999 [i.3].
TLS Transport Layer Security
T Time period equal to the maximum period of activation
MPA
TS Transport Stream
NOTE: As defined in ISO/IEC 13818-1 [1].
TTML Timed Text Markup Language
NOTE: As defined in W3C "Timed Text Markup Language 1 (TTML1)" [2].
TTS Text-To-Speech
uimsbf unsigned integer, most significant bit first
NOTE: When a uimsbf field is broken down into bit fields, the least significant bit is always referred to as b .
This will be the last bit of the field transmitted.
URI Uniform Resource Identifiers
NOTE: Generic form of DVB URI as defined in IETF RFC 3986 [21].
UTF Unicode Transformation Format
UTF-8 Unicode (or Universal Coded Character Set) Transformation Format - 8-bit
WOFF Web Open Font Format
NOTE: As defined in W3C Web Open Font Format (WOFF) 1.0 [18].
4 Default DVB TTML subtitle conformance point
4.1 Introduction
In order to maximize interoperability DVB has chosen a default DVB TTML document conformance point that can be
processed by either of two commonly used TTML processor profiles, EBU-TT-D [3] and IMSC1 [4] Text Profile.
4.2 Document Constraints
4.2.1 General
A DVB TTML subtitle stream conformant to the default conformance point shall be authored such that it can be
processed by an IRD supporting any of the following DVB TTML processor profile combinations:
• only EBU-TT-D [3], configured to meet the additional IRD requirements for the default conformance point in
clause 6.6;
• only IMSC1 [4] Text Profile;
• both EBU-TT-D [3] and IMSC1 [4] Text Profile.
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12 ETSI EN 303 560 V1.1.1 (2018-05)
The TTML profile identifier for the default conformance point from the TTML Profiles Registry [10] is described in
clause 5.2.1.1 as "etd1†|im1t", indicating that either a suitably constrained EBU-TT-D processor (etd1†) or an IMSC1
Text Profile processor (im1t) may be used.
The relationship between IMSC1 Text Profile and EBU-TT-D is explored in IMSC1 [4], annex I.2.
Certain differences between the EBU-TT-D and IMSC1 Text Profile TTML profiles are addressed by applying
additional constraints to IRDs, as opposed to further constraining TTML documents. These constraints apply to EBU-
TT-D processors compliant with the default conformance point:
• support IMSC1 generic font family name mapping, see clause 6.4;
• support IMSC1's default font colour of white, in the absence of any colour signalled, see clause 6.6;
• support itts:fillLineGap, ebutts:linePadding and ebutts:multiRowAlign style attributes, see clause 6.6;
• tolerate attributes in foreign namespaces, see clause 6.6;
• ignore unrecognised attributes, see clause 6.6.
The remaining differences between the EBU-TT-D and IMSC1 Text Profile TTML profiles are addressed through the
TTML document constraints specified in the following clauses. These constraints apply to TTML documents compliant
with the default conformance point.
4.2.2 Regions
In order to maintain IMSC1 conformance, a TTML subtitle stream shall have no more than four regions active at the
same time.
4.2.3 Document complexity
In order to maintain IMSC1 conformance, a TTML subtitle stream shall meet the requirements of the IMSC1 [4]
Hypothetical Render Model (HRM).
4.2.4 Document encoding
In order to maintain IMSC1 conformance, a TTML subtitle stream shall use UTF-8 encoding.
4.2.5 Namespaces
Documents compliant to the default conformance point shall only use namespaces as permitted in EBU-TT-D [3].
NOTE: Foreign namespaces are permitted within metadata elements because EBU-TT-D allows this.
4.2.6 Guidance for document authors and content providers (informative)
4.2.6.1 Overview
If a TTML document is authored to meet the default conformance points' document constraints with the intent of being
presented using a general purpose EBU-TT-D processor the following considerations may cause unexpected
presentation.
4.2.6.2 Font mapping for generic font family names
An EBU-TT-D processor configured to meet the default conformance point (see clause 6.6) could map a generic font
family name to a different font than a generic, EBU-TT-D processor would do, or an EBU-TT-D processor constrained ®
by other applicable specifications such as HbbTV as defined in ETSI TS 102 796 [5]. For example the
"proportionalSansSerif" generic font family could be mapped to the Arial font according to the default conformance ®
point, and the "default" generic font to Courier New, but an HbbTV EBU-TT-D implementation could map both to the
TM
Tiresias font.
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13 ETSI EN 303 560 V1.1.1 (2018-05)
If the document contents were authored with an equivalent to Arial as the intended presentation font and a font such as
TM
Tiresias is used, which generally produces text that occupies more width, unexpected line breaks or overflows could
be introduced.
NOTE: Tiresias™ is the trade name of a product supplied by Monotype. This information is given for the
convenience of users of the present document and does not constitute an endorsement by ETSI of the
product named. Equivalent products may be used if they can be shown to lead to the same results.
A possible workaround for unexpected line breaks is to author against the widest font that might be used for
presentation purposes. Alternatively the TTML profile signalling can be set to exclude use of processors that could
produce unexpected presentation.
4.2.6.3 Default text colour
Whilst generic TTML and EBU-TT-D processors are not required to set a default text colour, an IMSC1 Text profile
processor is required to adopt a default text colour of "white". It is therefore preferable to avoid doubt where consistent
presentation is important by specifying the colour of text explicitly within documents.
4.2.6.4 Requirement for support of optional features
An EBU-TT-D processor configured to meet the default conformance point (see clause 6.6) is required to support the
EBU-TT-D style attributes ebutts:multiRowAlign and ebutts:linePadding; a generic EBU-TT-D processor may not
support those attributes. This could result in unexpected positioning of subtitle text if those features are used and the
processor profile signalling permits rendering by a generic EBU-TT-D processor.
4.2.6.5 Specifying active area
IMSC1 [4] and EBU-TT-D [3] authors are recommended to use the ittp:activeArea attribute to indicate the area within
the root container that contains content that is intended to always be visible.
5 Delivery
5.1 IP delivery
The present document does not support delivery of subtitles over the Internet. ®
NOTE: The HbbTV specification as defined in ETSI TS 102 796 [5] provides a mechanism for synchronizing
EBU-TT-D [20] subtitles with broadcast video and audio. In that specification, EBU-TT-D [20] subtitles
can be delivered via MPEG-DASH segments using the DVB profile as defined in ETSI TS 103 285 [6] or
via a HTTP file download.
5.2 Broadcast TS delivery
5.2.1 PSI/SI signalling
5.2.1.1 TTML subtitling descriptor
The TTML subtitling descriptor presence in the ISO/IEC 13818-1 [1] PMT indicates that a PID contains a subtitle
stream conveyed using the PES structure defined in clause 5.2.2.2. The value of the stream_type in the PMT shall be
"0x06" indicating PES carrying private data.
This descriptor provides the following subtitle service properties:
• The ISO_639_language_code indicates the language of the subtitle service.
• The subtitle_purpose field indicates the intended purpose of the subtitle service.
ETSI
14 ETSI EN 303 560 V1.1.1 (2018-05)
• The TTS_suitability field indicates the suitability of the subtitles for conversion using a Text-To-Speech (TTS)
processor.
• The essential_font_usage_flag indicates if one or more downloadable fonts are required to present this subtitle
service.
Finally, the optional qualifier field provides additional informational presentation properties. It is defined below in
clause 5.2.1.3.
The TTML_subtitling_descriptor shall be coded according to table 1.
Table 1: TTML subtitling descriptor
Syntax Number of bits Identifier
TTML_subtitling_descriptor() {

descriptor_tag
8 uimsbf
descriptor_length
8 uimsbf
descriptor_tag_extension
8 uimsbf
ISO_639_language_code
24 bslbf
subtitle_purpose
6 uimsbf
TTS_suitability
2 uimsbf
essential_font_usage_flag
1 bslbf
qualifier_present_flag
1 bslbf
reserved_zero_future_use
2 bslbf
dvb_ttml_profile_count
4 uimsbf
for(i=0;i dvb_ttml_profile
8 uimbsf
}
if (qualifier_present_flag == 1){

qualifier
32 bslbf
}
if (essential_font_usage_flag == 1){
font_count
8 uimsbf
for(i=0; i reserved_zero_future_use
1 bslbf
font_id
7 uimsbf
}
}
text_length
8 bslbf
for(i=0;i text_char
8 bslbf
}
for(i=0;i reserved_zero_future_use
8 bslbf
}
}
Semantics for the TTML subtitling descriptor:
descriptor_tag: This 8-bit field shall have the value "0x7F" to indicate an extension_descriptor in accordance with
DVB BlueBook A038 [7].
descriptor_tag_extension: This 8-bit field shall have the value "0x20" in accordance with DVB BlueBook A038 [7].
ISO_639_language_code: This 24-bit field contains the ISO 639-2 [8] three character language code of the language of
the subtitles. Both ISO 639-2 [8]/B and ISO 639-2 [8]/T may be used. Each character is coded into 8-bits according to
ISO/IEC 8859-1 [9] and inserted in order into the 24-bit field.
EXAMPLE: French has 3-character code "fre", which is coded as:
"0110 0110 0111 0010 0110 0101".
subtitle_purpose: This 6-bit field signals the purpose of the subtitle service. Depending on the purpose, the subtitle
stream may include one or more features, as defined in table 2.
ETSI
15 ETSI EN 303 560 V1.1.1 (2018-05)
Table 2: Subtitle purpose
subtitle_p Short name Hard-of- Translation Non- Audio Content-
urpose hearing dialogue translation description related
dialogue commentary
0x00 same-lang-dialogue No No Yes No No
0x01 other-lang-dialogue No Yes No No No
0x02 all-dialogue No Yes Yes No No
0x03-0x0F reserved for future use
0x10 hard-of-hearing Yes No Yes No No
0x11 other-lang-dialogue- Yes Yes No No No
with-hard-of-hearing
0x12 all-dialogue-with-hard- Yes Yes Yes No No
of-hearing
0x13-0x2F reserved for future use
0x30 audio-description No No No Yes No
0x31 content-related- No No No No Yes
commentary
0x32-0x3F reserved for future use

The meaning of each of these features is as follows:
• Hard-of-hearing subtitle stream includes descriptions of non-dialogue sounds. (e.g. gun fire, explosion, lions
roar.)
• Translation dialogue subtitle stream includes a translation of foreign language dialogue.
• Non-translation dialogue subtitle stream includes a transcription of same language dialogue.
• Audio description subtitle stream includes description of the visual scene. (e.g. "a lion lies in the sun.")
• Content-related commentary subtitle stream includes commentary related information. (e.g. director's
commentary.)
TTS_suitability: This 2-bit field indicates whether the subtitles are suitable for text-to-speech (TTS) as described in
table 3.
Table 3: TTS suitability
TTS_suitability Meaning
0x0 unknown suitability for TTS
0x1 suitable for TTS
0x2 not suitable for TTS
0x3 reserved for future use
Only some subtitle streams are suitable for text-to-speech conversion and use as spoken subtitles. The typical use of
spoken subtitles is to provide an audible translation of "other language" dialogue into the viewer's preferred language,
so that viewers who are perhaps unable to read the presented subtitle text are nevertheless able to follow the programme
content. In addition, not all subtitles that are suitable for text-to-speech are also suitable for use as spoken subtitles; for
example, they could be intended for use as alternate sources of audio description. Table 4 illustrates the different
combinations.
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16 ETSI EN 303 560 V1.1.1 (2018-05)
Table 4: Example combinations of subtitle_purpose and TTS_suitability
TTS_suitability
Suitable for TTS Unknown suitability Not suitable for TTS
for TTS
Dialogue
Suitable for Spoken Possibly suitable for Not suitable for
(e.g. subtitle_purpose 0x00-0x02, 0x10-
Subtitles Spoken Subtitles Spoken Subtitles
0x12)
Hard-of-hearing Suitable for Possibly suitable for Not suitable as
(e.g. subtitle_purpose 0x10-0x12) alternative audio alternative audio alternative audio
source for hearing source for hearing source for hearing
impaired impaired impaired
Audio description Suitable for audio
Invalid combination Invalid combination
(e.g. subtitle_purpose 0x30)
...

SLOVENSKI STANDARD
01-september-2018
Digitalna videoradiodifuzija (DVB) - Sistemi TTML za podnaslove
Digital Video Broadcasting (DVB) - TTML subtitling systems
Ta slovenski standard je istoveten z: ETSI EN 303 560 V1.1.1 (2018-05)
ICS:
33.170 Televizijska in radijska Television and radio
difuzija broadcasting
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
Digital Video Broadcasting (DVB);
TTML subtitling systems
2 ETSI EN 303 560 V1.1.1 (2018-05)

Reference
DEN/JTC-DVB-375
Keywords
broadcast, digital, DVB, subtitle, TV

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All rights reserved.
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DECT , PLUGTESTS , UMTS and the ETSI logo are trademarks of ETSI registered for the benefit of its Members.
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3GPP and LTE are trademarks of ETSI registered for the benefit of its Members and
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GSM and the GSM logo are trademarks registered and owned by the GSM Association.
ETSI
3 ETSI EN 303 560 V1.1.1 (2018-05)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 6
Introduction . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 8
3 Definitions and abbreviations . 9
3.1 Definitions . 9
3.2 Abbreviations . 10
4 Default DVB TTML subtitle conformance point . 11
4.1 Introduction . 11
4.2 Document Constraints . 11
4.2.1 General . 11
4.2.2 Regions . 12
4.2.3 Document complexity . 12
4.2.4 Document encoding . 12
4.2.5 Namespaces . 12
4.2.6 Guidance for document authors and content providers (informative) . 12
4.2.6.1 Overview . 12
4.2.6.2 Font mapping for generic font family names . 12
4.2.6.3 Default text colour. 13
4.2.6.4 Requirement for support of optional features . 13
4.2.6.5 Specifying active area . 13
5 Delivery . 13
5.1 IP delivery . 13
5.2 Broadcast TS delivery . 13
5.2.1 PSI/SI signalling . 13
5.2.1.1 TTML subtitling descriptor . 13
5.2.1.2 Example TTML profile signalling . 17
5.2.1.2.1 Signalling conformance only to the default conformance point . 17
5.2.1.2.2 Signalling conformance to only EBU-TT-D . 17
5.2.1.2.3 Signalling conformance with EBU-TT-D and the default conformance point . 17
5.2.1.2.4 Signalling conformance to only IMSC1 Text Profile . 18
5.2.1.3 Presentation properties in qualifier field . 18
5.2.1.4 Component descriptors for TTML subtitles . 19
5.2.2 TS packetization . 19
5.2.2.1 PES packet format and carriage in the TS . 19
5.2.2.2 PES packet payload format for TTML subtitling . 20
5.2.2.2.1 General PES payload field syntax and segment types . 20
5.2.2.2.2 Occurrences of segments in one PES packet . 21
5.2.2.2.3 Uncompressed TTML document subtitle segment . 21
5.2.2.2.4 gzip compressed TTML document subtitle segment . 21
5.2.3 TTML segmentation . 21
5.2.3.1 General . 21
5.2.3.2 Concept of ISDs . 22
5.2.3.3 Active Period of a TTML segment . 22
5.2.3.4 TTML documents segmentation rules . 22
5.2.3.5 Subtitle stream in the absence of subtit les . 22
5.2.3.6 Continuation of a subtitle across adjacent segments . 22
5.2.3.7 Untimed elements in TTML segments . 23
5.2.3.8 Examples of TTML segmentation . 23
ETSI
4 ETSI EN 303 560 V1.1.1 (2018-05)
5.2.4 Synchronization . 23
5.2.4.1 Relationship between MPEG system clock and TTML timeline . 23
5.2.4.2 Failure of TTML segment reception . 24
5.2.4.3 Synchronization examples . 24
5.2.5 Acquisition time . 27
5.3 Font download . 27
5.3.1 Introduction. 27
5.3.2 Font delivery signalling mechanism . 28
5.3.2.1 Overview . 28
5.3.2.2 Linkage descriptor with linkage type 0x20 . 29
5.3.2.2.1 Introduction . 29
5.3.2.2.2 Linkage descriptor with linkage type 0x20 structure . 29
5.3.2.2.3 Linkage descriptor with linkage type 0x20 location, occurrence and prioritization . 30
5.3.2.3 Downloadable Font Information Table (DFIT) . 30
5.3.2.3.1 DFIT structure . 30
5.3.2.3.2 font_info_type in the loop of the DFIS . 32
5.3.3 IP download fonts . 33
5.3.4 Broadcast download fonts . 33
5.3.5 Downloaded font file, font name and font-id association . 33
6 IRD requirements . . 34
6.1 General support . 34
6.2 Forward compatibility . 34
6.3 Support of PSI/SI signalling and subtitle service selection . 34
6.3.1 PSI/SI signalling . 34
6.3.2 Determining which subtitle services can be rendered . 34
6.3.3 Subtitle service selection . 34
6.4 Font support in IRDs . 35
6.4.1 Supported fonts and font family name mapping . 35
6.4.2 Downloadable font retrieval . 35
6.4.3 Font selection for subtitle rendering . 36
6.5 Rendering requirements . 36
6.5.1 Playback free-running when A/V sync lost temporarily . 36
6.5.2 Behaviour during trick play . 36
6.5.3 Subtitle composition with HDR video . 36
6.5.4 Cropping and scaling of video . 37
6.6 Additional TTML processor requirements . 37
Annex A (informative): Change History . 38
History . 39

ETSI
5 ETSI EN 303 560 V1.1.1 (2018-05)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables 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 (https://ipr.etsi.org/).
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.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This European Standard (EN) 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: +41 22 717 21 11
Fax: +41 22 717 24 81
The Digital Video Broadcasting Project (DVB) is an industry-led consortium of broadcasters, manufacturers, network
operators, software developers, regulatory bodies, content owners and others committed to designing global standards
for the delivery of digital television and data services. DVB fosters market driven solutions that meet the needs and
economic circumstances of broadcast industry stakeholders and consumers. DVB standards cover all aspects of digital
television from transmission through interfacing, conditional access and interactivity for digital video, audio and data.
The consortium came together in 1993 to provide global standardization, interoperability and future proof
specifications.
ETSI
6 ETSI EN 303 560 V1.1.1 (2018-05)
National transposition dates
Date of adoption of this EN: 30 April 2018
Date of latest announcement of this EN (doa): 31 July 2018
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 31 January 2019
Date of withdrawal of any conflicting National Standard (dow): 31 January 2019

Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
Today's broadcast content can be distributed in many forms and via many different paths. Whilst broadcast services
traditionally relied on bitmap-based subtitles because of processing simplicity, advanced processing and text rendering
have made text-based approaches feasible. These offer more flexibility and better options to improve the user
experience. TTML (Timed Text Markup Language) is established as a common solution for IP-based platforms, but
multiple profiles exist.
In Europe, the EBU Group 'Subtitles in XML' published the EBU-TT-D TTML profile [20] which was adopted by the ®
DVB DASH specification as defined in ETSI TS 103 285 [6] and by HbbTV as defined in ETSI TS 102 79 [5]. The
W3C later published the IMSC1 TTML profiles [4], which were adopted by ATSC.
There are only minor differences between EBU-TT-D [3], [20] and IMSC1 Text Profile.
The present specification builds on the existing widespread device support for EBU-TT-D [20], in particular through ®
support for HbbTV , to enable the distribution of TTML subtitles together with audio/video content via broadcast.
Clause 4 specifies TTML subtitle constraints for a default conformance point, to be supported by both EBU-TT-D [3],
[20] and IMSC1 Text Profile compatible processors.
Clause 5 specifies subtitle delivery, including PSI/SI signalling, TS packetisation, TTML segmentation and
synchronization requirements.
Finally clause 6 specifies IRD requirements.

ETSI
7 ETSI EN 303 560 V1.1.1 (2018-05)
1 Scope
The present document specifies the transport of TTML [2] subtitle streams in DVB MPEG-2 transport streams,
based on the MPEG-2 system described in ISO/IEC 13818-1 [1]. TTML is an XML-based representation. The present
document provides syntax for delivery of TTML subtitle streams over MPEG-2 transport stream, and is based on
EBU-TT-D [3] compatible with the IMSC1 [4] Text Profile of W3C TTML [2].
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference/.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ISO/IEC 13818-1: "Information technology -- Generic coding of moving pictures and associated
audio information -- Part 1: Systems".
[2] W3C Recommendation (TTML): "Timed Text Markup Language 1 (TTML1) (Second Edition)".
NOTE: Available at http://www.w3.org/TR/2013/REC-ttml1-20130924/.
[3] EBU Tech 3380 "EBU-TT-D Subtitling Distribution Format", version 1.0.1.
NOTE: Available at https://tech.ebu.ch/publications/tech3380.
[4] W3C Recommendation (IMSC1): "TTML Profiles for Internet Media Subtitles and Captions 1.0.1
(IMSC1)".
NOTE: Available at http://www.w3.org/TR/ttml-imsc1.0.1/.
[5] ETSI TS 102 796: "Hybrid Broadcast Broadband TV".
[6] ETSI TS 103 285: "Digital Video Broadcasting (DVB); MPEG-DASH Profile for Transport of
ISO BMFF Based DVB Services over IP Based Networks".
[7] DVB BlueBook A038: "Digital Video Broadcasting (DVB); Specification for Service Information
(SI) in DVB systems".
NOTE: Available at http://www.dvb.org/resources/public/standards/a038_dvb_spec_december_2017.pdf.
[8] ISO 639-2: "Codes for the representation of names of languages -- Part 2: Alpha-3 code".
[9] ISO/IEC 8859-1: "Information technology -- 8-bit single-byte coded graphic character sets --
Part 1: Latin alphabet No. 1".
[10] W3C Working Group Note: "TTML Media Type Definition and Profile Registry".
NOTE: Available at http://www.w3.org/TR/ttml-profile-registry/.
[11] ETSI EN 301 192: "Digital Video Broadcasting (DVB); DVB specification for data broadcasting".
[12] ETSI TS 102 809: "Digital Video Broadcasting (DVB); Signalling and carriage of interactive
applications and services in hybrid broadcast/broadband environments".
ETSI
8 ETSI EN 303 560 V1.1.1 (2018-05)
[13] ETSI TS 102 851: "Digital Video Broadcasting (DVB); Uniform Resource Identifiers (URI) for
DVB Systems".
[14] IETF RFC 1952: "GZIP file format specification version 4.3".
[15] DVB BlueBook A126: "Digital Video Broadcasting (DVB); Allocation of identifiers and codes for
Digital Video Broadcasting (DVB) systems".
NOTE: Available at https://www.dvb.org/resources/public/standards/a126_allocation_identifiers.pdf.
[16] W3C Recommendation (XML): "Extensible Markup Language (XML) 1.0 (Fifth Edition)".
NOTE: Available at https://www.w3.org/TR/2008/REC-xml-20081126/.
[17] EBU Tech 3381: "Carriage of EBU-TT-D in ISOBMFF", version 1.0.
NOTE: Available at https://tech.ebu.ch/publications/tech3381.
[18] W3C Recommendation 13 December 2012 (WOFF): "Web Open Font Format (WOFF) 1.0".
NOTE: Available at http://www.w3.org/TR/2012/REC-WOFF-20121213/.
[19] ISO/IEC 14496-22:2015: "Information technology -- Coding of audio-visual objects --
Part 22: Open Font Format".
[20] EBU Tech 3380: "EBU-TT-D Subtitling Distribution Format", version 1.0.
NOTE: Available at https://tech.ebu.ch/publications/tech3380.
[21] IETF RFC 3986: "Uniform Resource Identifier (URI): Generic Syntax".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] W3C Recommendation (WCAG): "Web Content Accessibility Guidelines (WCAG) 2.0".
NOTE: Available at https://www.w3.org/TR/2008/REC-WCAG20-20081211/.
[i.2] W3C Candidate Recommendation (CSS): "CSS Fonts Module Level 3: Font matching algorithm".
NOTE: Available at https://www.w3.org/TR/css-fonts-3/#font-matching-algorithm.
[i.3] IEC 61966-2-1:1999: "Multimedia systems and equipment - Colour measurement and
management - Part 2-1: Colour management - Default RGB colour space - sRGB".
ETSI
9 ETSI EN 303 560 V1.1.1 (2018-05)
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
Intermediate Synchronic Document (ISD): temporally bounded (possibly empty) subset of TTML content during
which no elements change state between active and inactive
NOTE: A TTML document can conceptually be considered as a contiguous sequence of ISDs.
maximum period of activation (MPA): maximum duration a single TTML segment can be active, referred to as T
MPA
Packet IDentifier (PID): transport stream packet identifier
NOTE: See ISO/IEC 13818-1 [1].
PES packet: See ISO/IEC 13818-1 [1].
Presentation Time Stamp (PTS): See ISO/IEC 13818-1 [1].
reserved_zero_future_use: when used in the clause defining the coded bit stream, indicates that the value may be used
in the future for ETSI defined extensions
NOTE: All "reserved_zero_future_use" bits are set to "0".
subtitle segment: basic syntactical element of a subtitle stream
NOTE: The present document is structured to allow other types of subtitle segments to be defined in the future. In
this version of the specification, all subtitle segments are TTML segments.
subtitle service properties: properties defined by TTML subtitling descriptor which include but are not limited to
language, purpose, TTS_suitability, font usage, and qualifier
subtitle service: service that provides subtitling for an MPEG program (DVB service) with a set of subtitle service
properties
subtitle service qualifier variants: set of subtitle services whose subtitle service properties are identical except for
the qualifier_present_flag and qualifier fields in the TTML subtitling descriptor
subtitle stream: stream of subtitle segments carried in transport stream packets identified by the same PID,
containing a single subtitle service
transport stream packet: See ISO/IEC 13818-1 [1].
transport stream: stream of transport stream packets carrying one or more MPEG programs
NOTE: See ISO/IEC 13818-1 [1].
TTML document chunk: self-contained and temporally bounded subset of a TTML document [2]
NOTE: Self-contained in this context means that the document chunk contains all elements to render this subset
except the actual fonts used.
TTML segment: subtitle segment whose payload is an XML serialization of a TTML document chunk, concretely
encoded as a well-formed XML 1.0 [16] document
ETSI
10 ETSI EN 303 560 V1.1.1 (2018-05)
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ATSC Advanced Television Systems Committee
BAT Bouquet Association Table
bslbf bit string, left bit first
NOTE: The rightmost bit of a bslbf field is always referred to as b . This will be the last bit of the field
transmitted.
CRC Cyclic Redundancy Check
CSS Cascading Style Sheets
DASH Dynamic Adaptive Streaming over HTTP
DFIS Downloadable Font Information Section
DFIST Downloadable Font Information sub_table
DFIT Downloadable Font Information Table
DSI Download Server Initiate
DSM-CC Digital Storage Media - Command and Control
DVB Digital Video Broadcasting
DVB URI Uniform Resource Identifiers for DVB systems
NOTE: As defined in ETSI TS 102 851 [13].
EIT Event Information Table
NOTE: As defined in DVB BlueBook A038 [7]. ®
HbbTV Hybrid broadcast broadband TV
NOTE: As defined in ETSI TS 102 796 [5].
HDR High Dynamic Range
HRM Hypothetical Render Model
HTTP Hypertext Transfer Protocol
HTTPS Hypertext Transfer Protocol - Secure
IP Internet Protocol
IRD Integrated Receiver Decoder
ISD Intermediate Synchronic Document
MPA Maximum Period of Activation
MPEG Moving Pictures Experts Group
NIT Network Information Table
NOTE: As defined in ISO/IEC 13818-1 [1].
PES Packetized Elementary Stream
NOTE: As defined in ISO/IEC 13818-1 [1].
PID transport stream Packet IDentifier
NOTE: As defined in ISO/IEC 13818-1 [1].
PMT Program Map Table
NOTE: As defined in ISO/IEC 13818-1 [1].
PSI Program Specific Information
PTS Presentation Time Stamp
NOTE: As defined in ISO/IEC 13818-1 [1].
RGB Red Green Blue
ETSI
11 ETSI EN 303 560 V1.1.1 (2018-05)
SDT Service Description Table
NOTE: As defined in DVB BlueBook A038 [7].
SI Service Information
NOTE: As defined in ISO/IEC 13818-1 [1].
sRGB standard Red Green Blue
NOTE: As defined in IEC as IEC 61966-2-1:1999 [i.3].
TLS Transport Layer Security
T Time period equal to the maximum period of activation
MPA
TS Transport Stream
NOTE: As defined in ISO/IEC 13818-1 [1].
TTML Timed Text Markup Language
NOTE: As defined in W3C "Timed Text Markup Language 1 (TTML1)" [2].
TTS Text-To-Speech
uimsbf unsigned integer, most significant bit first
NOTE: When a uimsbf field is broken down into bit fields, the least significant bit is always referred to as b .
This will be the last bit of the field transmitted.
URI Uniform Resource Identifiers
NOTE: Generic form of DVB URI as defined in IETF RFC 3986 [21].
UTF Unicode Transformation Format
UTF-8 Unicode (or Universal Coded Character Set) Transformation Format - 8-bit
WOFF Web Open Font Format
NOTE: As defined in W3C Web Open Font Format (WOFF) 1.0 [18].
4 Default DVB TTML subtitle conformance point
4.1 Introduction
In order to maximize interoperability DVB has chosen a default DVB TTML document conformance point that can be
processed by either of two commonly used TTML processor profiles, EBU-TT-D [3] and IMSC1 [4] Text Profile.
4.2 Document Constraints
4.2.1 General
A DVB TTML subtitle stream conformant to the default conformance point shall be authored such that it can be
processed by an IRD supporting any of the following DVB TTML processor profile combinations:
• only EBU-TT-D [3], configured to meet the additional IRD requirements for the default conformance point in
clause 6.6;
• only IMSC1 [4] Text Profile;
• both EBU-TT-D [3] and IMSC1 [4] Text Profile.
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12 ETSI EN 303 560 V1.1.1 (2018-05)
The TTML profile identifier for the default conformance point from the TTML Profiles Registry [10] is described in
clause 5.2.1.1 as "etd1†|im1t", indicating that either a suitably constrained EBU-TT-D processor (etd1†) or an IMSC1
Text Profile processor (im1t) may be used.
The relationship between IMSC1 Text Profile and EBU-TT-D is explored in IMSC1 [4], annex I.2.
Certain differences between the EBU-TT-D and IMSC1 Text Profile TTML profiles are addressed by applying
additional constraints to IRDs, as opposed to further constraining TTML documents. These constraints apply to EBU-
TT-D processors compliant with the default conformance point:
• support IMSC1 generic font family name mapping, see clause 6.4;
• support IMSC1's default font colour of white, in the absence of any colour signalled, see clause 6.6;
• support itts:fillLineGap, ebutts:linePadding and ebutts:multiRowAlign style attributes, see clause 6.6;
• tolerate attributes in foreign namespaces, see clause 6.6;
• ignore unrecognised attributes, see clause 6.6.
The remaining differences between the EBU-TT-D and IMSC1 Text Profile TTML profiles are addressed through the
TTML document constraints specified in the following clauses. These constraints apply to TTML documents compliant
with the default conformance point.
4.2.2 Regions
In order to maintain IMSC1 conformance, a TTML subtitle stream shall have no more than four regions active at the
same time.
4.2.3 Document complexity
In order to maintain IMSC1 conformance, a TTML subtitle stream shall meet the requirements of the IMSC1 [4]
Hypothetical Render Model (HRM).
4.2.4 Document encoding
In order to maintain IMSC1 conformance, a TTML subtitle stream shall use UTF-8 encoding.
4.2.5 Namespaces
Documents compliant to the default conformance point shall only use namespaces as permitted in EBU-TT-D [3].
NOTE: Foreign namespaces are permitted within metadata elements because EBU-TT-D allows this.
4.2.6 Guidance for document authors and content providers (informative)
4.2.6.1 Overview
If a TTML document is authored to meet the default conformance points' document constraints with the intent of being
presented using a general purpose EBU-TT-D processor the following considerations may cause unexpected
presentation.
4.2.6.2 Font mapping for generic font family names
An EBU-TT-D processor configured to meet the default conformance point (see clause 6.6) could map a generic font
family name to a different font than a generic, EBU-TT-D processor would do, or an EBU-TT-D processor constrained ®
by other applicable specifications such as HbbTV as defined in ETSI TS 102 796 [5]. For example the
"proportionalSansSerif" generic font family could be mapped to the Arial font according to the default conformance ®
point, and the "default" generic font to Courier New, but an HbbTV EBU-TT-D implementation could map both to the
TM
Tiresias font.
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13 ETSI EN 303 560 V1.1.1 (2018-05)
If the document contents were authored with an equivalent to Arial as the intended presentation font and a font such as
TM
Tiresias is used, which generally produces text that occupies more width, unexpected line breaks or overflows could
be introduced.
NOTE: Tiresias™ is the trade name of a product supplied by Monotype. This information is given for the
convenience of users of the present document and does not constitute an endorsement by ETSI of the
product named. Equivalent products may be used if they can be shown to lead to the same results.
A possible workaround for unexpected line breaks is to author against the widest font that might be used for
presentation purposes. Alternatively the TTML profile signalling can be set to exclude use of processors that could
produce unexpected presentation.
4.2.6.3 Default text colour
Whilst generic TTML and EBU-TT-D processors are not required to set a default text colour, an IMSC1 Text profile
processor is required to adopt a default text colour of "white". It is therefore preferable to avoid doubt where consistent
presentation is important by specifying the colour of text explicitly within documents.
4.2.6.4 Requirement for support of optional features
An EBU-TT-D processor configured to meet the default conformance point (see clause 6.6) is required to support the
EBU-TT-D style attributes ebutts:multiRowAlign and ebutts:linePadding; a generic EBU-TT-D processor may not
support those attributes. This could result in unexpected positioning of subtitle text if those features are used and the
processor profile signalling permits rendering by a generic EBU-TT-D processor.
4.2.6.5 Specifying active area
IMSC1 [4] and EBU-TT-D [3] authors are recommended to use the ittp:activeArea attribute to indicate the area within
the root container that contains content that is intended to always be visible.
5 Delivery
5.1 IP delivery
The present document does not support delivery of subtitles over the Internet. ®
NOTE: The HbbTV specification as defined in ETSI TS 102 796 [5] provides a mechanism for synchronizing
EBU-TT-D [20] subtitles with broadcast video and audio. In that specification, EBU-TT-D [20] subtitles
can be delivered via MPEG-DASH segments using the DVB profile as defined in ETSI TS 103 285 [6] or
via a HTTP file download.
5.2 Broadcast TS delivery
5.2.1 PSI/SI signalling
5.2.1.1 TTML subtitling descriptor
The TTML subtitling descriptor presence in the ISO/IEC 13818-1 [1] PMT indicates that a PID contains a subtitle
stream conveyed using the PES structure defined in clause 5.2.2.2. The value of the stream_type in the PMT shall be
"0x06" indicating PES carrying private data.
This descriptor provides the following subtitle service properties:
• The ISO_639_language_code indicates the language of the subtitle service.
• The subtitle_purpose field indicates the intended purpose of the subtitle service.
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14 ETSI EN 303 560 V1.1.1 (2018-05)
• The TTS_suitability field indicates the suitability of the subtitles for conversion using a Text-To-Speech (TTS)
processor.
• The essential_font_usage_flag indicates if one or more downloadable fonts are required to present this subtitle
service.
Finally, the optional qualifier field provides additional informational presentation properties. It is defined below in
clause 5.2.1.3.
The TTML_subtitling_descriptor shall be coded according to table 1.
Table 1: TTML subtitling descriptor
Syntax Number of bits Identifier
TTML_subtitling_descriptor() {

descriptor_tag
8 uimsbf
descriptor_length
8 uimsbf
descriptor_tag_extension
8 uimsbf
ISO_639_language_code
24 bslbf
subtitle_purpose
6 uimsbf
TTS_suitability
2 uimsbf
essential_font_usage_flag
1 bslbf
qualifier_present_flag
1 bslbf
reserved_zero_future_use
2 bslbf
dvb_ttml_profile_count
4 uimsbf
for(i=0;i dvb_ttml_profile
8 uimbsf
}
if (qualifier_present_flag == 1){

qualifier
32 bslbf
}
if (essential_font_usage_flag == 1){
font_count
8 uimsbf
for(i=0; i reserved_zero_future_use
1 bslbf
font_id
7 uimsbf
}
}
text_length
8 bslbf
for(i=0;i text_char
8 bslbf
}
for(i=0;i reserved_zero_future_use
8 bslbf
}
}
Semantics for the TTML subtitling descriptor:
descriptor_tag: This 8-bit field shall have the value "0x7F" to indicate an extension_descriptor in accordance with
DVB BlueBook A038 [7].
descriptor_tag_extension: This 8-bit field shall have the value "0x20" in accordance with DVB BlueBook A038 [7].
ISO_639_language_code: This 24-bit field contains the ISO 639-2 [8] three character language code of the language of
the subtitles. Both ISO 639-2 [8]/B and ISO 639-2 [8]/T may be used. Each character is coded into 8-bits according to
ISO/IEC 8859-1 [9] and inserted in order into the 24-bit field.
EXAMPLE: French has 3-character code "fre", which is coded as:
"0110 0110 0111 0010 0110 0101".
subtitle_purpose: This 6-bit field signals the purpose of the subtitle service. Depending on the purpose, the subtitle
stream may include one or more features, as defined in table 2.
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Table 2: Subtitle purpose
subtitle_p Short name Hard-of- Translation Non- Audio Content-
urpose hearing dialogue translation description related
dialogue commentary
0x00 same-lang-dialogue No No Yes No No
0x01 other-lang-dialogue No Yes No No No
0x02 all-dialogue No Yes Yes No No
0x03-0x0F reserved for future use
0x10 hard-of-hearing Yes No Yes No No
0x11 other-lang-dialogue- Yes Yes No No No
with-hard-of-hearing
0x12 all-dialogue-with-hard- Yes Yes Yes No No
of-hearing
0x13-0x2F reserved for future use
0x30 audio-description No No No Yes No
0x31 content-related- No No No No Yes
commentary
0x32-0x3F reserved for future use

The meaning of each of these features is as follows:
• Hard-of-hearing subtitle stream includes descriptions of non-dialogue sounds. (e.g. gun fire, explosion, lions
roar.)
• Translation dialogue subtitle stream includes a translation of foreign language dialogue.
• Non-translation dialogue subtitle stream includes a transcription of same language dialogue.
• Audio description subtitle stream includes description of the visual scene. (e.g. "a lion lies in the sun.")
• Content-related commentary subtitle stream includes commentary related information. (e.g. director's
commentary.)
TTS_suitability: This 2-bit field indicates whether the subtitles are suitable for text-to-speech (TTS) as described in
table 3.
Table 3: TTS suitability
TTS_suitability Meaning
0x0 unknown suitability for TTS
0x1 suitable for TTS
0x2 not suitable for TTS
0x3 reserved for future use
Only some subtitle streams are suitable for text-to-speech conversion and use as spoken subtitles. The typical use of
spoken subtitles is to provide an audible translation of "other language" dialogue into the viewer's preferred language,
so that viewers who are perhaps unable
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