Mixed Signals’ Approachto Encoding DTV Closed Captions

Mixed Signals’ Approachto Encoding DTV Closed Captions

Line 21Line 21NTSCNTSC

CaptionsCaptions

TranscoderTranscoder DTVCCDTVCCCaptionsCaptions

““Legacy”Legacy”CaptionsCaptions

EIA-608EIA-608

EIA-708EIA-708

Transcoding

Transcoding at Time-of-Air

AdvantagesAdvantages

• Uses existing line 21 captionsUses existing line 21 captions

• Technique currently in use by dozens of DTV Technique currently in use by dozens of DTV broadcastersbroadcasters

• Works with both Standard Definition and HD Works with both Standard Definition and HD programsprograms

• Low costLow cost

Application #1

Time-of-Air EncodingTime-of-Air EncodingFrom D1 SourceFrom D1 Source

Application #2

Time-of-Air EncodingTime-of-Air EncodingFrom Composite SourceFrom Composite Source

DTV 708Closed Caption

Data Server

SerialDigital

Interface

CompositeVideo

Interface

DTVUpconverter

DTVEncoder /Transport

Multiplexer

AnalogVideo In

MonitorVideo Out

AnalogComposite

Video,NTSC or PAL

CompositeVideo

Monitor

Decoded Captions /On-screen Menus

Video

Data

Application #3

HDTV Live or Off-LineHDTV Live or Off-LineEncodingEncoding

SMPTE 333M Interface

DTV Closed Caption Server to ATSC Encoder InterfaceDTV Closed Caption Server to ATSC Encoder Interface

ObjectivesObjectives

• Ensure captions are displayed at exactly the time Ensure captions are displayed at exactly the time intended by caption creatorintended by caption creator

• Guarantee all four NTSC caption bytes are transmitted Guarantee all four NTSC caption bytes are transmitted each pictureeach picture

• Maintain allowed DTVCC transport rate of 9600 bpsMaintain allowed DTVCC transport rate of 9600 bps

• Minimize complexity on part of DTV encoder/transport Minimize complexity on part of DTV encoder/transport multiplexermultiplexer

DTV 708 DTVCC Data Server

DTV 708Features

>Built-in closed caption decoder, LTC time code reader, bidirectional GPI

>Easy to use on-screen menus

>Optional modem, LAN interface

>Able to read caption files including emerging native EIA-708 files

Thank You!Thank You!

What can we do to helpWhat can we do to helpDTVCC closed captioning?DTVCC closed captioning?