Overview: Broadcast captions
Broadcast captions use defined services and signaling to carry timed text and related presentation information.
A caption service belongs to the broadcast signal's organization, with its own selection and rendering rules. The standards below cover different service arrangements and character or presentation capabilities. SCC adds a stored interchange representation to that picture, so a caption service and a subtitle sidecar are not assumed to be the same object.
Closed-caption services
A closed-caption service is a selectable timed content stream whose commands, characters and presentation state must be recovered from its carrying media.CEA-608 / CTA-608
CTA-608 describes legacy line-21 caption data with channel selection, character/control codes and a cell-based presentation model that can also be carried digitally.CEA-708 / CTA-708
CTA-708 describes digital caption services with window, pen, text and visibility commands, alongside separate 608 compatibility carriage.Teletext subtitles
Teletext subtitles select a caption page whose character/control data, row updates and broadcast signaling establish the timed display.ARIB STD-B24 captions
ARIB STD-B24 captions combine coded characters, display controls and resources such as DRCS glyphs under their applicable broadcast profile.Scenarist Closed Captions (SCC)
SCC stores timecoded hexadecimal 608 caption words whose decoder commands determine the actual visible caption presentation.