IEC 62731:2013

IEC 62731


®


Edition 1.0 2013-01



INTERNATIONAL



STANDARD



NORME
INTERNATIONALE


Text-to-speech for television – General requirements

Synthèse vocale pour télévision – Exigences générales


IEC 62731:2013

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IEC 62731



®



Edition 1.0 2013-01







INTERNATIONAL





STANDARD







NORME



INTERNATIONALE











Text-to-speech for television – General requirements



Synthèse vocale pour télévision – Exigences générales




















INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE

PRICE CODE
INTERNATIONALE

CODE PRIX R


ICS 33.160.25; 33.160.99 ISBN 978-2-83220-600-3



Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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– 2 – 62731 © IEC:2013



CONTENTS

FOREWORD . 3


1 Scope . 5

2 Normative references . 5

3 Terms, definitions and abbreviations . 5


3.1 Terms and definitions . 5

3.2 Abbreviations . 7

4 Guiding principles and conventions . 7

5 User requirements of visually impaired people . 7
5.1 Users' needs . 7
5.2 Navigating channels . 8
5.3 Navigating TV inputs . 8
5.4 Additional data services . 8
5.5 Operating the TV . 8
5.6 TV use . 9
6 Functional requirements . 9
6.1 Functionality for TV, TTS device combination . 9
6.2 Functionality: TTS device/engine . 10
6.3 Functionality: TV . 10
6.4 Setting up: TV, TTS device combination . 10
7 TV events and TTS data . 11
7.1 TV context and events . 11
7.2 TTS data per event . 12
7.2.1 Details . 12
7.2.2 Channel change . 12
7.2.3 Additional information . 13
7.2.4 Navigation and selection . 13
7.2.5 Context switch . 14
7.2.6 Pop-up message. 15
8 TTS profiles . 16
8.1 Basic profile . 16
8.2 Main profile . 16
8.3 Enhanced profile . 17

8.4 Summary . 17
Bibliography . 19

Figure 1 – TV – TTS device system diagram . 9
Figure 2 – Context event state diagram . 12

Table 1 – Overview of profiles . 18

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62731 © IEC:2013 – 3 –


INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________



TEXT-TO-SPEECH FOR TELEVISION –

GENERAL REQUIREMENTS





FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62731 has been prepared by IEC technical committee 100: Audio,
video and multimedia systems and equipment.

The text of this standard is based on the following documents:
FDIS Report on voting
100/2070/FDIS 100/2109/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

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The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be


• reconfirmed,

• withdrawn,

• replaced by a revised edition, or

• amended.

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62731 © IEC:2013 – 5 –


TEXT-TO-SPEECH FOR TELEVISION –

GENERAL REQUIREMENTS







1 Scope



This International Standard specifies the text-to-speech functionality for a (broadcast) receiver
with a text-to-speech system. Such a system may be one device, i.e. a receiver with an

integrated text-to-speech generator, or may be two devices, i.e. a receiver interfacing with an

external text-to-speech device. This International Standard applies only to completely
functional stationary (or semi-stationary) digital TV receivers such as set top boxes,
integrated digital TVs, recorders and other products whose primary function is to receive TV
content. Where this standard refers to TV, this will be shorthand for all such receivers.
This International Standard does not apply to products that are capable of receiving TV as a
secondary function (e.g. PCs or game consoles with digital television receivers). It also does
not apply to sub-assemblies (e.g. PC tuner cards).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
(void)
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
context
one specific function of a TV
EXAMPLE Watching TV, EPG, etc.

3.1.2
DTV broadcast event
set of related broadcast streams with a defined start and end time, commonly referred to as a
TV programme
Note 1 to entry: DTV events have typically the following properties associated with them: start time, end time or
duration, content synopsis, additional content information, parental rating and availability of subtitles or audio
description.
3.1.3
DTV service information
metadata describing broadcasting content and its scheduling and timing details
Note 1 to entry: The purpose of DTV service information is to aid the end user to select and schedule viewing and
recording, and also to select the equipment configuration.

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3.1.4

DTV broadcast event classification

general category of programme/event content, or its classification


EXAMPLES Movie (drama), news/current affairs, talk show, sports (football), etc.


3.1.5
EPG filter

filter that organises or reduces the list of displayed EPG items according to certain criteria


EXAMPLES Of criteria are to show only:

• programmes with a certain content type;
• favourites;
• programmes that are audio described;
• programmes for a given time period (for instance "today", "tomorrow", "next 7 days").
3.1.6
event
trigger to start an action
3.1.7
list
collection of items
3.1.8
menu
subsequent order of items
3.1.9
receiver
device capable of receiving or handling digital television signals
3.1.10
service
sequence of programs under the control of a broadcaster which can be broadcast as part of a
schedule
3.1.11
subtitle
textual representation of the dialogue (and frequently additional auditory information),
typically shown at the bottom of the screen

Note 1 to entry: Subtitles can be a textual rendering in the same language as the spoken dialogue, or can provide
a written translation in a different language.
Note 2 to entry: In some parts of the world subtitles are called "(closed) captions", and subtitling is referred to as
"(closed) captioning".
Note 3 to entry: This standard uses the term subtitles throughout.
3.1.12
TTS audio
audio output by the TTS engine in correspondence with TTS data
Note 1 to entry: If the TV uses an external TTS converter, TTS audio is interpreted as TTS data.
3.1.13
TTS data
(text) data converted into TTS audio information by the text-to-speech engine

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62731 © IEC:2013 – 7 –


3.2 Abbreviations


For the purposes of this document, the following abbreviations apply.

DTV digital television

EPG electronic programme guide

STB set top box

TTS text-to-speech


TV television

UI user interface

4 Guiding principles and conventions
This standard describes the required basic behaviour for a TV text-to-speech combination in a
basic profile, but also provides for enhanced profiles. It also gives a short introduction into the
basic problems of visually impaired people: i.e. what are the problems visually impaired
people experience when using and watching TV?
Providing text-to-speech functionality for a broadcast receiver, e.g. TV or STB can be of great
help to (visually) disabled people. Such speech functionality may be integrated in the receiver
or may be external to the receiver in a separate device.
In general as the guiding principle, when building a TTS interface in the context of this
standard, implementers should aspire to achieve functional equivalence of the user
experience. This means that a person operating the device using the speech interface should
have access to similar information and be able to accomplish similar tasks as with a graphical
UI.
The main features of this International Standard are:
• basic functional description for a TV-TTS device combination or TV with integrated TTS;
• profiles for different levels of TV-TTS functionality;
• targeted towards the digital TV application.
In this standard mandatory requirements are specified; optional and informative features are
also included.
A claim of conformity with this standard requires conformity with all mandatory requirements.
A TV-TTS device combination or a TV with a TTS that is integrated may provide options for a

user to enable or disable product features.
5 User requirements of visually impaired people
5.1 Users' needs
This subclause 5.1 explains the needs of visually impaired people as the primary target users
for a TV with TTS. Unless these needs are met, the system is not accessible to this user
group. Visually impaired people experience access barriers in the course of the following
activities when watching TV:
a) following TV programming, e.g. the TV series;
b) using a remote control;
c) not being able to see subtitles;
d) navigating channels;

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e) navigating TV inputs;

f) using additional data (text) services provided by the broadcaster, e.g. an EPG;


g) daily operation of the TV and initial setup of the TV for use.

Items a), b) and c) are outside the scope of this standard. Item c) further relates to the fact

that in some countries foreign language programmes are being translated via subtitles. For

users who cannot see the subtitles, supplementary audio services are sometimes used to

deliver an audio version of the subtitles. This standard elaborates on the remaining four items,

i.e. d), e), f) and g), in 5.2 to 5.6.


NOTE 1 For DVB systems, item a) is already solved by audio description. Also, the use case of providing

supplementary audio services to deliver an audio version of the subtitles is covered in the DVB-SI specification
ETSI EN 300 468.
NOTE 2 For ATSC systems, the audio system includes a visually impaired (VI) associate service which allows a
complete programme mix containing music, effects, dialogue, and additionally a narrative description of the picture
content, see ATSC A/53 part 5 and part 6.
5.2 Navigating channels
The problem is a user does not know which channel the TV displays, i.e. the user gets “lost
during navigation”. The TV is displaying navigation data on the screen but the user is unable
to see it. Such data are for example:
• channel number,
• service name,
• (DTV broadcast) event name.
5.3 Navigating TV inputs
The problem is that a user is unable to select the required input to the TV, e.g. the user
wishes to select DTV or a specific external input linked to a recording or other device. The
choice is shown on the screen but the user is unable to see it.
5.4 Additional data services
With digital TV a broadcaster may transmit additional data (text) services to augment TV
programming, provide additional information on programming, or provide news. Such
additional data are:
• information about whether audio description, subtitling is available,
• (next) (DTV broadcast) event name,
• (DVB-) event information (enhanced description of the (DTV broadcast) event),

• EPG data.
The items above are listed in order of importance with the most important item appearing first.
It is noted that this data provides additional convenience in using the TV, but that is non-
essential for the primary function of watching TV, and selecting channels.
5.5 Operating the TV
User settings are another needed function besides navigation. This can be done through
buttons on the remote control (out of scope for this specification), but also via on-screen
menus. For visually impaired people on-screen menus are typically of little use.
A distinction exists between initial setup and daily operation of the TV. Initial setup is typically
a onetime operation during the lifetime of a TV. Daily operation is more frequent and more
important. Consequently a distinction among menu items for daily operation exists, those
addressing specific accessibility functions, and TV setup menu items. However, the most
frequently used keys are “volume”, “channel up/down”, and number keys.

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62731 © IEC:2013 – 9 –


5.6 TV use


Use characterization of a TV helps in determining implementation profiles. Navigating

channels, for example, is done most often when watching TV, as well as commands like

volume up and down. This may be supported by additional data services, but does not affect

the primary functions of the TV. Changing the TV's system settings is not done very often,
except perhaps for changing sound or video settings or switching audio description on and off.

Such settings may have an easy access mode through a special menu. TV installation is

typically performed only once during the lifetime of the TV. Often, visually impaired people

can benefit from specialized support for installing the TV, i.e. it is part of the service when

buying a new TV. Understanding this life- and usage cycle of a TV helps with defining the

most effective and efficient solutions and is reflected in the profiles. In the following

paragraphs, we refer to “basic”, “main” and “enhanced” profiles as further defined and
detailed in Clause 8.
Key operations for a minimum TTS implementation on a receiver for TV use are as set out in
the basic profile defined in this standard. This basic profile shall include:
a) channel number, name and event information – key for a user to identify which service
has been selected;
b) availability of audio description – key for a user to know about the availability of this
service feature;
c) availability of subtitles – key for a user to know about the availability of this service
feature;
d) basic EPG – allow the user to navigate through the EPG, if such data is present in the
broadcast, to identify which future events are available to them;
e) context changes – key for a user to understand if the TV went to another state or when a
pop-up message appears;
f) the main profile shall in addition to all the items from the basic profile include receiver
menu functions (allows the user to navigate receiver operations and functions).
Additional operations that shall be included in the enhanced profile, in addition to all those
from the basic and main profiles, are:
g) event Information – provide the event synopsis;
h) additional EPG data – allows the user to get more info on the service or event;
i) operations of a recording device – allows the user to record future events, possibly
selected via the EPG. Play/pause a recorded event.
6 Functional requirements

6.1 Functionality for TV, TTS device combination


Text to

speech
TV
device
IEC  187/13

Figure 1 – TV – TTS device system diagram
The TV-TTS device system diagram is illustrated in Figure 1. As shown in the figure the TTS
device is a separate function from the TV, which can be implemented on a device connected
with a TV-TTS device interface, or may also be integrated in the TV.

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The functionality requirements for a TV with TTS combination are:


• the delay between an event and the resulting TTS audio related to that event shall be such

that they are perceived as belonging tied together;

• priority TTS audio shall overrule currently playing TTS audio information;

• the user should be able to stop currently playing TTS audio;

• the user shall be able to repeat the current or previous TTS audio;

• the user shall be able to mute the TTS audio;

• the user shall be able to switch on/off the TTS function;

• the language of the TTS audio shall be the same as set for the TV’s UI, except when
signalled differently. The TTS device/engine may choose to pronounce the text or to
indicate failure in case it does not support the signalled language;
• TTS audio may not need to literally represent the related visual information on the screen
as long as the meaning of the visual information stays intact.
6.2 Functionality: TTS device/engine
The TV, in principle, only outputs text strings towards the TTS device.
The TTS device shall follow these outputs:
• an external TTS device should be designed to be fully accessible to visually impaired
users without being dependent on the TV;
• the volume level of the TTS device/engine shall be changeable by the user. The TTS
device shall announce the new volume level. It should be possible to do this independent
from the TV volume;
• the user should be able to adjust speech characteristics like speed, pitch, voice type,
when applicable;
• the TTS engine should announce abbreviations as such, letter by letter, rather than as a
normal word. Example: “TTS” should be announced “T T S” (“tee tee es”) instead of “tts”
(“tetes”) where relevant. The TTS engine may also pronounce common acronyms in full,
e.g. “sub” could be spoken as “subtitles” where appropriate This standard does not identify
what is understood to be an abbreviation, rather leaves this at the discretion of
implementers;
• the TTS engine should announce numbers in a manner suited to the context, e.g. as
natural number, digit-by-digit, etc.;
• the TTS engine is considered to determine the context.

6.3 Functionality: TV
The TV determines the user interface, i.e. what is displayed on the screen, and how the TV
interacts with the user. The TV therefore also determines which text is sent to the TTS engine.
The user should be able to control, via the TV TTS, settings like volume, speed, pitch, voice
type.
NOTE In Europe, to fulfil basic accessibility needs, the TV is expected to comply with SELFC.
6.4 Setting up: TV, TTS device combination
TTS audio g
...