Mixed Signals’ Approach to Encoding DTV Closed Captions Mixed Signals’ Approach to Encoding DTV Closed Captions

Line 21 NTSCCaptions Transcoder DTVCCCaptions “Legacy”Captions EIA-608 EIA-708 Transcoding

Transcoding at Time-of-Air Advantages Uses existing line 21 captionsUses existing line 21 captions Technique currently in use by dozens of DTV broadcastersTechnique currently in use by dozens of DTV broadcasters Works with both Standard Definition and HD programsWorks with both Standard Definition and HD programs Low costLow cost

Application #1 Time-of-Air Encoding From D1 Source

Application #2 Time-of-Air Encoding From Composite Source

Application #3 HDTV Live or Off-Line Encoding

SMPTE 333M Interface DTV Closed Caption Server to ATSC Encoder Interface Objectives Ensure captions are displayed at exactly the time intended by caption creatorEnsure captions are displayed at exactly the time intended by caption creator Guarantee all four NTSC caption bytes are transmitted each pictureGuarantee all four NTSC caption bytes are transmitted each picture Maintain allowed DTVCC transport rate of 9600 bpsMaintain allowed DTVCC transport rate of 9600 bps Minimize complexity on part of DTV encoder/transport multiplexerMinimize complexity on part of DTV encoder/transport multiplexer

DTV 708 DTVCC Data Server DTV 708 Features > >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

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