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Implementing Closed Captioning Implementing Closed Captioning for DTVfor DTV

Graham JonesGraham JonesNABNAB

Broadcast Engineering ConferenceBroadcast Engineering ConferenceApril, 2004April, 2004

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Agenda

• Terminology • FCC rules• Standards• Carriage of DTV closed captions• PSIP and the caption service descriptor

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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

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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

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So, what’s the difference?

608 line 21608 line 21

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Native 708Native 708

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Native 708Native 708

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Translated 708 DTVCC Translated 708 DTVCC –– as encodedas encoded

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DTV caption menuDTV caption menu

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Translated 708 DTVCC Translated 708 DTVCC –– user formatuser format

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Translated 708 DTVCC Translated 708 DTVCC –– user formatuser format

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Translated 708 DTVCC Translated 708 DTVCC –– user formatuser format

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Translated 708 DTVCC Translated 708 DTVCC –– user formatuser format

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AmendedAmendedPart 15Part 15

andandPart 79Part 79

of the FCC Rulesof the FCC Rules

FCC rules for DTVCCFCC rules for DTVCCReport and OrderReport and Order

0000--259259July 21, 2000July 21, 2000

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Part 15.122Part 15.122Decoders forDecoders forDTV receiversDTV receivers

Effective July 2002Effective July 2002

Part 79.1Part 79.1Closed captionsClosed captions

for DTVfor DTVprogrammingprogramming

Phased schedulePhased schedule

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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

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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 highdefinition and standard definition

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FCC Rules – New Programming

1/1/02 – 12/31/03 900 hours/quarter1/1/04 – 12/31/05 1350 hours/quarterAfter 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

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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

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FCC Rules – Pre-rule Programming1/1/03 – 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

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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

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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

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SMPTE Standards• SMPTE 333M

– DTV Closed-Caption Server to Encoder Interface• SMPTE 334M

– Vertical Ancillary Data Mapping for Bit-Serial Interface

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ATSC Standards• ATSC A/53B Digital Television Standard

– Carriage of DTVCC in the ATSC transport• ATSC A/65B PSIP Standard

– Caption Service Descriptor (CSD)

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Recommended Implementation

708 DTV caption data608 compatibility bytesCaption service descriptor in EIT (and PMT for cable)

All these elements should be carried in the ATSC bitstreamFor distribution upstream of the ATSC encoder they can be carried in a caption distribution packet (CPD) defined in CEA-708-B

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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

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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)

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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)

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Encoder embeds CDPs in VANC as perSMPTE 334M

Currently used only for 292M HD signals

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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

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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

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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

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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

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PSIP EIT must contain the caption service descriptor to announce and describe the services present

Serial link for 708 data into the 708 encoder

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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

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Monitoring

• The written paper discusses various requirements for 708 caption monitoring– Presence– Display/functionality– Synchronization– Regulatory compliance

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708 Equipment

• Four known vendors for 708 encoders

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708 Authoring Software

• Coming soon…

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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

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Sources of Information

• Caption Central–– www.www.captioncentralcaptioncentral.com.com

• Closed Captioning Handbookby Gary Robson, Focal Press

• NCAM – DTV Access Project–– www.dtvaccess.orgwww.dtvaccess.org

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DTV Draft House

• Demonstration of 708 closed captioningby NCAM

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SMPTE EG 43SMPTE EG 43Trial publication on web siteTrial publication on web sitewww.smpte.orgwww.smpte.organd for sale on CDand for sale on CD--ROMROM

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Acknowledgements

• SMPTE• Gerry Field, NCAM• John Demshock, WFTV• Rudy Pruitt, PBS• Members of the ATSC Closed

Captioning Working Group

Thank yougjones@nab.orggjones@nab.org