COMM. Closed captioning. "CC in a TV" symbol was created at WGBH.
Terminology[edit] The term "closed" (versus "open") indicates that the captions are not visible until activated by the viewer, usually via the remote control or menu option. "Open", "burned-in", or "hard-coded" captions are visible to all viewers. The United Kingdom, Ireland, and most other countries do not distinguish between subtitles and closed captions, and use "subtitles" as the general term—the equivalent of "captioning" is usually referred to as "subtitles for the hard of hearing". Their presence is referenced on screen by notation which says "Subtitles", or previously "Subtitles 888" or just "888" (the latter two are in reference to the conventional teletext channel for captions), which is why the term subtitle is also used to refer to the Ceefax based Teletext encoding that is used with PAL-compatible video. History [edit] Open captioning[edit] Technical development of closed captioning[edit]
EIA-608. EIA-608, also known as "line 21 captions" and "CEA-608",[1] used to be the standard for closed captioning for NTSC TV broadcasts in the United States, Canada and Mexico.
It also specifies an "Extended Data Service", which is a means for including a VCR control service with a now/next EPG for NTSC transmissions that operates on the even line 21 field, similar to the TeleText based VPS that operates on line 16 which is used in PAL countries. It was developed by the Electronic Industries Alliance and required by law to be implemented in most television receivers made in the United States. Raw EIA-608 caption byte pairs are becoming less prevalent as digital television replaces analog. ATSC broadcasts instead use the EIA-708 caption protocol to encapsulate both the EIA-608 caption pairs as well as a native EIA-708 stream.
Channels[edit] EIA-608 defines four channels of caption information, so that a program could, for example, have captions in four different languages. Characters[edit] Teletext. History[edit] Invention & Design[edit] In the early 1970s work was in progress in Britain that would transmit paged information within a television broadcast.
While engineers in several organisations were developed the equipment that would be used to transmit and receive the information. The work progressed at relatively the same pace as the U.S. developed EIA-608 caption only format. The goal was to provide UK rural homes with electronic hardware that could download pages of up-to-date news, reports, facts and figures targeting the U.K. farming communities. The invention and design that became the basis of all Teletext and similar systems was created in 1971 by the Philips Lead Designer for VDUs, John Adams. A major objective for Adams during the concept development stage was to make Teletext affordable to the home user. Development[edit] Rollout[edit] North America[edit] Screenshot of an Electra teletext page.
World System Teletext[edit] CEA-708. CEA-708 is the standard for closed captioning for ATSC digital television (DTV) streams in the United States and Canada.
It was developed by the Electronic Industries Alliance. Unlike RLE DVB and DVD subtitles, CEA-708 captions are low bandwidth textual like traditional EIA-608 captions and EBU Teletext/Ceefax subtitles. However, unlike EIA-608 byte pairs, CEA-708 captions are not able to be modulated on an ATSC receiver's NTSC VBI line 21 composite output and must be pre-rendered by the receiver with the video frames, they also include more of the Latin-1 character set, and include stubs to support full UTF-32 captions, and downloadable fonts. CEA-708 caption decoders are required in the U.S. by FCC regulation in all 13" (33 cm) diagonal or larger digital televisions. Further, some broadcasters are required by FCC regulations to caption a percentage of their broadcasts. Packets in CEA-708[edit] Caption streams are transmitted with many packet wrappers around them. Picture User Data[edit]