What kind of closed captioning is supported by standard definition DTV (ATSC) video?
DTV requires both CEA-708 and CEA-608 closed captioning data, stored as metadata packets within the DTV stream, whether the video is standard definition or high definition. For typical standard definition sources ingested from SD tape, the station will generate the packets by up-converting from the line 21 data on the tape, in the video encoding stage just before DTV transmission. If you are sending a SD tape for DTV broadcast, you only need regular line 21 closed captions. However, if you will deliver a standard definition MPEG-2 transport stream that is ready for broadcast (bypassing the encoder stage), you must encode your file with both CEA-708 and CEA-608 caption data. There is a third standard for digital SD closed captions known as SCTE-20, which preceded the DTV closed captioning standard. Some older cable set-top boxes (STBs) only support SCTE-20 and not the newer DTV standard. Cable networks which have deployed these STBs may require that MPEG-2 transport streams delivered fo
