CEA-708 (Consumer Electronics Association-708), also called EIA-708 is the current standard for closed captioning (textual transcription of the audio content of a program) for Advanced Television Systems Committee (ATSC) digital television (DTV) streams in the United States and Canada. It was developed by the Electronic Industries Alliance.
Unlike run-length encoding digital video broadcasting (RLE DVB) and DVD subtitles, CEA-708 captions are low bandwidth textual like traditional CEA-608 captions and EBU Teletext/Ceefax subtitles. Building upon the prior CEA-608 standard, CEA-708 has support for more character sets and better caption positioning options.
CEA-708 captions are injected into MPEG-2 video streams in the picture user data. The packets are in picture order, and must be rearranged just like picture frames are. This is known as the DTVCC Transport Stream. It is a fixed-bandwidth channel that accommodates backward compatible line-21 captions and CEA-708 captions. The main form of signalling is via a PSIP caption descriptor which indicates the language of each caption and is formatted for easy reader (3rd grade level for language learners) in the Program and system Information Protocol (PSIP) event information table (EIT) on a per event basis.
CEA-708 caption decoders are required in the U.S. by Federal Communications Commission regulation in all 13-inch diagonal or larger digital televisions. Some broadcasters are required by FCC regulations to caption a percentage of their broadcasts.
CEA-608, also known as EIA-608 and line-21 captions, is the former standard for closed captioning for NTSC (National Television System Committee) TV broadcasts in the United States, Canada and Mexico. It was developed by the Electronic Industries Alliance and was required by law to be implemented in most television receivers made in the United States. Scenarist Closed Caption (SCC), file extension .scc is the preferred file format when captions are based on CEA-608 features.
CEA-608 captions are transmitted on either the odd or even fields of line 21 with an odd parity bit in the non-visible active video data area in NTSC broadcasts and are also sometimes present in the picture user data in ATSC transmissions. The odd field captions relate to the primary audio track and the even field captions related to the second audio program (SAP), usually a second-language translation of the primary audio, such as a French or Spanish translation of an English-speaking TV show. CEA-608 was later revised with the addition of extended character sets to fully support the representation of the Spanish, French and other Western European languages, as well as to support two-byte characters for the Korean and Japanese markets.