| 摘要 |
a transmitter for transmitting a digital broadcast signal comprises a multiplexer for multiplexing audio, video and control data to output a DTV stream, and a transmitter. The video data includes user data bits carrying a DTVCC transport channel including caption carrying data for providing a closed caption service. the contol data includes a program mapping table and an event information table, one of which includes a caption service descriptor containning a caption information field indicating whether a DTV closed caption service or a line 21 closed caption service is present in the video data in accordance with EIA 708. The caption information field is set when the closed caption service is present and clear when the line 21 closed caption service is present in accordance with EAI 708. A caption service number in the caption service desciptor is only defined when the DTV closed caption service is present. |
