Implementing Closed Captioning Implementing Closed Captioning
for DTV for DTV
Graham Jones Graham Jones
NABNAB
Broadcast Engineering Conference Broadcast Engineering Conference
April, 2004 April, 2004
Agenda
• Terminology
• FCC rules
• Standards
• Carriage of DTV closed captions
• PSIP and the caption service descriptor
Terminology
• DTV – ATSC broadcast, also cable and DBS
• DTVCC – closed captions for DTV
• CEA-608-B – standard for analog NTSC captioning
• CEA-708-B – standard for DTV captioning
Terminology
• Native 708
– DTVCC encoded and transmitted in the 708 format in which they were authored
• Translated or Derived 708
– 708 DTVCC translated from line 608 line 21 legacy captions
– Sometimes misleadingly referred to as “upconverted”
– Sometimes misleadingly referred to as “transcoded”
• Transcoded 608
– 608 line 21 data may be transcoded to fill required 608 compatibility bytes in the 708 caption distribution
So, what’s the difference?
608 line 21 608 line 21
Native 708 Native 708
Native 708 Native 708
Translated 708 DTVCC
Translated 708 DTVCC –– as encodedas encoded
DTV caption menu DTV caption menu
Translated 708 DTVCC
Translated 708 DTVCC –– user formatuser format
Translated 708 DTVCC
Translated 708 DTVCC –– user formatuser format
Translated 708 DTVCC
Translated 708 DTVCC –– user formatuser format
Translated 708 DTVCC
Translated 708 DTVCC –– user formatuser format
Amended Amended
Part 15 Part 15
andand Part 79 Part 79
of the FCC Rules of the FCC Rules
FCC rules for DTVCC FCC rules for DTVCC
Report and Order Report and Order
00-00-259259
July 21, 2000 July 21, 2000
Part 15.122 Part 15.122 Decoders for Decoders for DTV receivers DTV receivers Effective July 2002 Effective July 2002
Part 79.1 Part 79.1
Closed captions Closed captions
for DTV for DTV
programming programming Phased schedule Phased schedule
FCC Rules Summary
• Since July 2002, DTV receivers with >7.8” screen height, and STBs, must have caption decoders
complying with section 9 of CEA-708-B, with some optional features defined as mandatory
• CEA-708-B is incorporated by reference into the rules
• STBs with NTSC output must output 608 captions in line 21
FCC Rules Summary
• Part 79 now says transmitted closed captions must reflect the changes in Part 15, i.e. DTV programs must include CEA-708-B captions
• During the transition 708 captions may be translated from existing 608 caption data
• Multi-channel program distributors receiving
programs with CEA-708-B captions must deliver to the home with that captioning intact
No distinction between DTVCC for high definition and standard definition
FCC Rules – New Programming
1/1/02 – 12/31/03 900 hours/quarter 1/1/04 – 12/31/05 1350 hours/quarter
After 1/1/06 100% (some exceptions)
• New digital programming is “prepared or formatted for display on digital televisions, that was first
published or exhibited after July 1, 2002”
• Spanish language schedule leads to 100% by 2010
Exemptions
• Programs shown 2 a.m.- 6 a.m.
• Commercials no longer than five minutes
• Programs not in English or Spanish
• Local non-news programming
• Some local PBS instructional programming
• Several other program types
FCC Rules – Pre-rule Programming
1/1/03 – 12/31/07 30% of programming (1/1/05 for Spanish)
After 1/1/08 75% of programming (1/1/12 for Spanish)
• Pre-rule programming is that first published or exhibited before July 1, 2002”
• So DTV services now have the same hourly captioning requirements as NTSC services
CEA Standards
• CEA-608-B
– closed captioning and data for line 21 of NTSC signals
• CEA-708-B
– DTV closed captions only for ATSC bitstreams
– Defines format of 708 DTV captions, decoders, and encoding of 708 data and 608 compatibility bytes in the DTV bitstream
– Other information, e.g. caption service descriptor, parental guidance, and other program information previously carried in VBI, is carried in PSIP
SCTE Standards
• SCTE 43
– Digital Video Systems Characteristics for Cable TV – Requires DTV captions to be encoded in
accordance with CEA-708-B and transported in accordance with A/53B
• SCTE 54
– Digital Video Service Multiplex and Transport for Cable TV
– When captions are delivered in A/53B, then the caption service descriptor shall be present in the PMT and in the EIT, if present
SMPTE Standards
• SMPTE 333M
– DTV Closed-Caption Server to Encoder Interface
• SMPTE 334M
– Vertical Ancillary Data Mapping for Bit-Serial Interface
ATSC Standards
• ATSC A/53B Digital Television Standard
– Carriage of DTVCC in the ATSC transport
• ATSC A/65B PSIP Standard
– Caption Service Descriptor (CSD)
Recommended Implementation
9 708 DTV caption data 9 608 compatibility bytes
9 Caption service descriptor in EIT (and PMT for cable)
¾ All these elements should be carried in the ATSC bitstream
¾ For distribution upstream of the ATSC encoder
they can be carried in a caption distribution packet (CPD) defined in CEA-708-B
Caption Encoding and Distribution
• Analog and DTV captions are quite different in the way they are encoded, distributed, and transmitted
• For NTSC, captions are usually encoded,
distributed, and transmitted on line 21 of the video signal
Carriage of 708 Captions
• 708 captions for DTV have different methods for carriage before and after the ATSC encoder. They may be carried:
– in ATSC video user data bits for emission (A/53B)
– on serial data link from a caption encoder to the ATSC encoder (SMPTE 333M and Grand Alliance standard) – embedded as CDP in serial digital video VANC for
recording and distribution (SMPTE 334M)
– multiplexed in an AES3 data stream (SMPTE 337M)
Carriage of 708 Captions
• 708 captions for DTV have different methods for carriage before and after the ATSC encoder. They may be carried:
– in ATSC video user data bits for emission (A/53B)
– on serial data link from a caption encoder to the ATSC encoder (SMPTE 333M and Grand Alliance standard) –– embedded as CDP in serial digital video VANC for embedded as CDP in serial digital video VANC for
recording and distribution (SMPTE 334M) recording and distribution (SMPTE 334M)
– multiplexed in an AES3 data stream (SMPTE 337M)
Encoder
embeds CDPs in VANC as per SMPTE 334M Currently used only for 292M HD signals
Recording, Processing, Distribution
• VANC captions are “sticky data” and
follow video through most baseband routing and switching equipment
• Care needed with preserving VANC data through VTRs, servers and production
switchers and DVEs
• Data bridges
• Issues of latency
Compression Distribution Systems
• HD program distribution from networks to affiliates or member stations typically use compressed video over satellite
– must extract captions from VANC – place in private data PID, or
– in A/53B video user data
• IRDs are available that re-insert captions in
VANC for distribution at the station
Local Station Arrangements
• The written paper shows various scenarios for handling DTV captions at the station
– 708 captions from the network – Locally generated 708
– Translated from 608
– Up and down video format conversion
• VANC is most common distribution method, but use of a caption server at the station with local encoding is an alternative
Caption Input to the ATSC Encoder
• External VANC disembedder
– SMPTE 333M / Grand Alliance interface – Caption service descriptor
• Increasing use of internal VANC disembedder from 292M video
• An alternative architecture uses a caption
encoder or translator feeding the ATSC
encoder direct
PSIP EIT must contain the caption service
descriptor to announce and describe the
services present Serial link for
708 data into the 708 encoder
PSIP and Caption Service Descriptor
• For EITs for future events, CSD will need to come from program schedule/listing
service
• For “current event” EIT and PMT, it is
preferable for CSD to come from the on-air program CDP or live caption encoder
– Actual captions could be different from scheduled captions
Monitoring
• The written paper discusses various
requirements for 708 caption monitoring
– Presence
– Display/functionality – Synchronization
– Regulatory compliance
708 Equipment
• Four known vendors for 708 encoders
708 Authoring Software
• Coming soon…
Conclusions
• FCC rules require DTV 708 captions now
• Products are available from several manufacturers
• Make sure your bitstream contains both 708 and 608 data and the CSD in EIT and PMT
• Legal 708 DTV captioning is achievable using captions translated from 608
• Producers need to move to native 708 caption authoring
Sources of Information
• Caption Central
–– www.www.captioncentralcaptioncentral.com.com
• Closed Captioning Handbook
by Gary Robson, Focal Press
• NCAM – DTV Access Project
–– www.dtvaccess.orgwww.dtvaccess.org
DTV Draft House
• Demonstration of 708 closed captioning
by NCAM
SMPTE EG 43 SMPTE EG 43
Trial publication on web site Trial publication on web site
www.smpte.org www.smpte.org
and for sale on CD
and for sale on CD--ROMROM
Acknowledgements
• SMPTE
• Gerry Field, NCAM
• John Demshock, WFTV
• Rudy Pruitt, PBS
• Members of the ATSC Closed Captioning Working Group
Thank you