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CEA-608 and CEA-708 closed captions

OpenSaveBroadcastIn the video

The closed captions of North American television. CEA-608 comes from analog TV: two bytes a frame, in line 21 of the picture. CEA-708 is its digital successor, with windows, colours and many services. A digital broadcast carries both in every frame. Subtitld reads them from a video, and writes them in SCC and MCC files.

At a glance

SpecificationCTA-608 (formerly EIA-608, then CEA-608) and CTA-708 (formerly CEA-708). In digital video, ATSC A/53 Part 4.
Where they travelIn the video's frames, in a caption track of their own (QuickTime's c608), and in SCC and MCC files
Time precisionA frame
CharactersCEA-608: its own Latin set. CEA-708: ASCII, Latin-1, a few symbols, and 16-bit characters.
StylingCEA-608: italics, underline, seven colours. CEA-708: italics, underline, 64 colours, fonts, sizes, edges and backgrounds.
PositioningCEA-608: a grid of 15 rows of 32 columns. CEA-708: up to eight windows, anchored on a grid of 75 rows.
ChannelsCEA-608: CC1 to CC4. CEA-708: up to 63 services.
SpeakersNone in the standards. Captioners write >> at each change of speaker.

A frame's caption data

Each frame carries a few sets of three bytes. The first byte of each says what the other two are.

FC 94 2F
FD 80 80
FF 42 22
FE 89 01
FA 00 00 …
  1. 1 · What follows

    FC is CEA-608's first field, FD its second. FF starts a CEA-708 packet, and FE carries it on.

  2. 2 · CEA-608

    Two bytes for each field. 94 2F shows the caption loaded in CC1; 80 80 is nothing.

  3. 3 · CEA-708

    A packet, two bytes at a time: its header (42, four bytes long), a service block's (22, service 1, two bytes), then 89 01, DisplayWindows for window 0.

  4. 4 · Room

    The frame's other sets, carrying nothing. A frame has 20 at 29.97 frames a second, 25 at 24, 24 at 25.

9,600 bits a second for captions. The caption channel of a digital broadcast keeps 960 of them for the CEA-608 it carries along, which converter boxes pass on to analog TVs, and 8,640 for CEA-708.

CEA-608: four channels

The bytes are the ones an SCC file holds: commands and characters, two a frame, on a screen of 15 rows of 32 columns. Each of the picture's two fields carries two caption channels.

Channel Where Use
CC1 Field 1, first channel The programme's captions
CC2 Field 1, second channel Another language, or nothing
CC3 Field 2, first channel Often a second language
CC4 Field 2, second channel Rarely used

CEA-708: windows and pens

A CEA-708 service draws in windows: up to eight, each with its place, its size, its rows and its style, shown, hidden, toggled and deleted. A pen writes in them, with italics, underline and colours. These load a caption and show it:

Bytes Command
98 18 DA 32 70 13 09 DefineWindow 0 Hidden, its bottom centre 90% down and 50% across the screen, one row of 20 columns
88 01 ClearWindows Window 0, empty
97 C0 00 0E 00 SetWindowAttributes No fill behind it, the text centred
92 00 00 SetPenLocation Row 0, column 0
90 05 00 SetPenAttributes Standard size, upright, not underlined
91 3C 00 00 SetPenColor Yellow, on black
59 6F 75 … You're a jerk,
90 05 00 91 3F 00 00 The pen again White, on black
20 54 68 … Thom.
89 01 DisplayWindows Window 0, in the frame the caption starts

The window's anchor is one of nine points, its corners, the middle of its sides and its centre: the nine places a subtitle can sit in Subtitld.

Characters What they hold
G0 ASCII, but for its delete, which is ♪
G1 Latin-1: the accents of Western European languages
G2 A few more: … ‘ ’ “ ” • ™ Š Œ ⅛ ⅜ ⅝ ⅞ and box drawing
P16 Characters of 16 bits, as Korean captions use

Captions in a video

Where Who puts them there How Subtitld reads them
In the frames: MPEG-2 user data, H.264 and HEVC SEI Digital broadcasts, and recordings of them (.ts) Decoding the video, as long as that takes
A caption track (c608) QuickTime deliveries At once
An SCC file Broadcast and streaming deliveries CEA-608
An MCC file Broadcast deliveries, MacCaption CEA-708, else CEA-608

CEA-608 / 708 in Subtitld

Kept
  • Every caption's text and line breaks
  • Italics and underline
  • Colours: seven in CEA-608, 64 in CEA-708
  • Where it sits: top, middle or bottom; left, centre or right
  • Speakers, as >> at each change
  • Start and end, to the frame
Nowhere to go
  • Bold, which neither has
  • CEA-708's fonts, sizes, edges and window backgrounds
  • More than one service or channel at a time: read one, then another
  • Translations beside the original

Save a .usfx project to keep what is Subtitld's.

Reading the captions of a video

Subtitld's Import panel with the captions engine chosen, reading the first captions the video has, CEA-708 before CEA-608
In the Import panel, choose the captions engine, then Read captions. Captions in the video's frames take as long to read as the video takes to decode; a caption track is read at once.

It offers:

  • CaptionsThe first the video has, CEA-708 before CEA-608; a CEA-708 service, 1 to 6; or a CEA-608 channel, CC1 to CC4.
  • ScopeThe whole video, a range of it, or the selected subtitle, as for a transcription.

Subtitld decodes them as a decoder does. A caption loaded out of sight and shown is a subtitle until it is hidden, cleared or replaced. Captions written live on screen, line by line, become a subtitle a line, until the next line begins. Times are counted from the start of the video. A video with no captions says so.

Recordings of broadcasts come as .ts, .m2ts or .mts files, which Subtitld opens as video.

Writing them

Subtitld writes captions in the files broadcasters and platforms take:

  • SCC: pop-on captions in CEA-608, CC1;
  • MCC: the same in CEA-608 and, in step with them, in CEA-708's service 1, or CEA-608 alone if you choose.

Trivia

2002

From 1 July 2002, digital TVs sold in the United States, all but the smallest, had to decode CEA-708 captions: the six standard services at least.

8

Windows a CEA-708 service can have at once, each with its own place, size and style. CEA-608 has one screen.

CC

CEA-708's characters include the closed-caption logo itself, the CC that marks a captioned programme, among its extended ones.

Related formats

Have a recording with captions?

Open it in Subtitld, read its captions into the timeline, and fix and retime them on the waveform.

Download Subtitld