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SMPTE
Engineering Guideline on Closed Captioning Implementation
The Federal
Communications Commission's (FCC) rules require broadcasters to
provide closed captioning for most programming, in accordance
with the CEA-708 standard. The technical requirements for this
are rather complex and require reference to multiple documents
from ATSC, CEA, SMPTE and SCTE. To provide guidance for system
integrators and broadcasters, in 2004 the Society of Motion Picture
and Television Engineers (SMPTE) published an engineering guideline
for system implementation of closed captioning. The guideline
has been updated in a SMPTE Technology Committee group led by
an NAB Science and Technology department staff members and will
shortly be published by SMPTE as EG 43-2009, System Implementation
of CEA-708 and CEA-608 Closed Captioning and Program-Related Data.
Updates to
the guideline reflect changes in the standards for carriage of
caption data in the ancillary data space of baseband video signals.
It also now mentions caption carriage in ATSC AVC video streams
and for ATSC Mobile DTV, and reflects the addition of several
SCTE caption-related standards. Updated and expanded sections
provide information and guidance on topics that include: the carriage
of multiple caption services, adding additional captions after
initial authoring, generation and distribution of the caption
service descriptor, ensuring consistency of 708 and 608 caption
services, what 608 XDS program-related has to be included and
consistency with PSIP data.
The following
Introduction, Scope and Table of Contents are reproduced with
permission from SMPTE. The new EG43-2009 will be available in
the near future, from: https://store.smpte.org/.
Introduction
This
section is entirely informative and does not form an integral
part of the Engineering Document.
Specifications
for closed captioning for NTSC analog television broadcasting1
are set out in the CEA-608 standard. Production, distribution
and insertion of captioning information to meet these requirements
have been implemented for many years using a combination of standards-based
and accepted-practice techniques.
Specifications
for closed captioning for ATSC digital television (DTV) in the
United States are set out in the CEA-708 standard. The term DTV
in CEA-708 includes and applies to HDTV (high definition digital
television) and SDTV (standard definition digital television)
that use the digital data stream specified in ATSC A/53. CEA-708
captions are also specified for use in ATSC standard A/72 for
AVC (Advanced Video Coding), in SCTE cable systems for both AVC
(ANSI/SCTE 128) and SMPTE VC-1 (SCTE 157), as well as in ATSC
A/153 for Mobile/ DTV.
During the
transition from analog to digital broadcasting, analog NTSC and
DTV transmissions will coexist, as will analog and digital cable
distribution systems. After the closure of NTSC transmissions,
analog and digital television production and distribution systems
will possibly coexist in many facilities and networks, frequently
with both standard definition (SD) and high definition (HD) video
formats. This situation creates added complexity for closed captioning
as well as other aspects of system implementation. In addition,
some multichannel video program distribution systems will continue
to distribute NTSC analog signals and in some cases such signals
are derived by conversion from ATSC DTV signals (see ATSC A/79
for more information). In other cases, NTSC signals will be derived
from ATSC DTV signals by a consumer digital converter box.
CEA-708 specifies
standards for encoding and decoding DTV closed captions (DTVCC)
but provides little guidance on system design and interfacing
for DTVCC in broadcast systems.
[Footnote
1: NTSC broadcasting from full-power NTSC stations in the United
States ended in June 2009 but NTSC transmissions from low-power
stations and translators will continue for some time after that
date. NTSC broadcasts also continue in other countries.]
Scope
The primary purpose of this guideline is to provide guidance for
system implementation of closed captioning for DTV as defined
in CEA-708, concentrating on different techniques that are required
for DTVCC implementation when compared to CEA-608 captioning systems
for NTSC. It also provides guidance on distribution of certain
program-related data carried in the CEA-608 data construct. It
identifies the relevant standards that exist for different parts
of the system and, where possible, indicates guidelines for areas
that are not standardized.
This guideline describes methods that can be used to support the
various links in the chain from caption creation through to emission.
Consideration is given to systems that support captioning for
SD and HD program material, which can originate and/or be distributed
in standard formats as used in broadcasting and related facilities.
While CEA-708 refers specifically to DTV implemented for main
stream ATSC broadcast systems, techniques described herein are
applicable for programming for other DTV environments such as
ATSC Mobile DTV and cable or satellite distribution.
In this guideline,
transport for distribution of DTVCC within the broadcast plant
is based primarily on the use of SMPTE 334-1, which define a method
of embedding DTVCC and other data services in the vertical ancillary
(VANC) data space of video signals conforming with SMPTE 292 high-definition
serial digital interface (HD-SDI) or SMPTE 259M serial digital
interface (SDI). HD-SDI in this guideline refers to bit-serial
component 1080 or 720 line television signals. SDI in this guideline
refers to bit-serial component 525-line television signals. The
carriage of DTVCC over serial data links in accordance with SMPTE
333 or RP 2007 is also included, together with arrangements for
distributing caption service information. Reference is made to
alternative server-based methods of distributing and managing
closed captioning.
A method for
carriage of DTVCC caption data in an AES3 data stream is specified
in SMPTE 337M. Further details of that arrangement are not described
here.
Table
of Contents
1 Scope
2 References
3 Terms and Acronyms
3.1 Acronyms and Abbreviations
3.2 Terms
4 Closed Captioning Standards
4.1 Relevant CEA Standards
4.2 Relevant SMPTE Standards
4.3 Relevant ATSC Standards
4.4 Relevant SCTE Standards
4.5 Relevant DVB/ETSI Standards
5 System Configurations
6 Caption Creation and Encoding
6.1 Captioning Process
6.2 CEA-608 Caption Encoding
6.3 CEA-708 Caption Encoding
6.4 CEA-708 Caption Encoding Feeding Direct to the MPEG Encoder
6.5 CEA-708 Caption Translation within the MPEG Encoder Using
CEA-608 Captions from Line 21
6.6 Required Level of Implementation
6.7 Adding Additional DTV Captions after Initial Caption Authoring
7 Recording, Processing and Routing
7.1 Recording
7.2 VANC Data Bridge
7.3 Video Processing
7.4 Switching Considerations
8 Contribution and Distribution
8.1 Tape Interchange
8.2 File-based Delivery
8.3 Contribution/Distribution Compression Systems
9 Emission
9.1 NTSC Output
9.2 ATSC Station Output
9.3 Captioning Inputs to an MPEG Emission Encoder
9.4 Captioning in AVC Bitstreams
9.5 Captioning for ATSC Mobile DTV
9.6 Local Live DTV Captions
9.7 NTSC – DTV (up-conversion)
9.8 DTV – NTSC (down-conversion)
9.9 Completeness of CEA-608 Captions, Text, and Program data
9.10 Consistency of CEA-708 and CEA-608 Caption Services
9.11 Consistency of XDS Data and PSIP Data
9.12 ANSI/SCTE 127 Data
9.13 Server-based Captionig
9.14 Caption Service Descriptor
10 Monitoring
10.1 608 Caption Monitoring
10.2 708 Caption Monitoring
Annex A Bibliography (Informative)
Annex B Descriptor enquiry message format (Informative)
Annex C Field-marked message format for CEA-608 data (Informative)
NAB
Hosts Satellite Uplink Operators Training Seminar
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| Shown
(left to right) are Dan Feliz, Southwest Sound; Michael Miller,
NASA; Angela McKinley, U.S. Naval Observatory; Sidney Skjei,
course instructor, Skjei Telecom; and Bill Hull, director,
satellite operations, PBS. |
Last week,
NAB hosted the NAB Satellite Uplink Operators Seminar at NAB headquarters
in Washington, D.C. In addition to classroom
course work, the seminar includes hands-on training with a satellite
uplink truck provided this year by WJLA in Washington, D.C. and
a visit to the PBS Satellite Operations Center shown in the photo
to the right. Sidney Skjei of Skjei Telecom is the course instructor.
NAB has trained
more than 600 engineers and technicians from radio and television
stations, universities and satellite services from across the
U.S. and abroad, including engineers from China, Europe and Mexico.
Look for the upcoming announcement on the 2010 class schedule.
2010 NAB Show Call for Speakers
Call
for Technical Papers – NAB Broadcast Engineering Conference
The
2010 NAB Show will host the 64th Broadcast Engineering Conference.
This world-class conference addresses the most recent developments
in broadcast technology and focuses on the opportunities and challenges
that face broadcast engineering professionals. Each year hundreds
of broadcast professionals from around the world attend the conference.
They include practicing broadcast engineers and technicians, engineering
consultants, contract engineers, broadcast equipment manufacturers,
distributors, R&D engineers plus anyone specifically interested
in the latest broadcast technologies.
Do you have something to share?
If you feel qualified to speak at the NAB Broadcast Engineering
Conference, we invite you to submit
a technical paper proposal. Not all acceptable submissions can
be included in the conference, due to the large number of submissions
that are received and the limited number of available time slots.
PLAN TO ATTEND!
The IEEE
Broadcast Technology Society
59th ANNUAL BROADCAST SYMPOSIUM
October 14 -16, 2009
The Westin Alexandria
Alexandria, VA, USA
www.ieee.org/bts/symposium
2009 ATSC Seminar on Audio Loudness
Wednesday, November 4, 2009
Wiley Rein Conference Center
1776 K St, NW
Washington, DC 20006
http://www.atsc.org/seminars/loudness09.php
Cost for ATSC members is $50.00 for pre-registrants, $75.00 on-site.
The
October 12, 2009 TV TechCheck is also available
in an Adobe Acrobat file.
Please
click here to read the Adobe Acrobat version of TV
TechCheck.
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