EIA-608

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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.

EIA-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. It uses a fixed bandwidth of 480 bit/s per line 21 field for a maximum of 32 characters per line per caption (maximum four captions) for a 30 frame broadcast. The odd field captions relate to the primary audio track and the even field captions related to the SAP or secondary audio track which is generally a second language translation of the primary audio, such as a French or Spanish translation of an English-speaking TV show.

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. EIA-608 has had revisions with the addition of extended character sets to fully support the representation of the Spanish, French, German languages, and cross section of other Western European languages. EIA-608 was also extended to support two byte characters for the Korean and Japanese markets. The full version of EIA-708 has support for more character sets and better caption positioning options; however, because of existing EIA-608 hardware and revisions to the format, there has been little or no real world use of the format besides simple 608 to 708 inline conversions.

Channels[edit]

EIA-608 defines four channels of caption information, so that a program could, for example, have captions in four different languages. There are two channels, called 1 and 2 by the standard, in each of the two fields of a frame. However, the channels are often presented to users numbered simply as CC1-2 for the odd field and CC3-4 for the even field. However due to bandwidth limitations on either field, CC1 and CC3 are the only ones used, meaning that there has been little use for the second channel. Early Spanish SAP captioned broadcasts first used the second channel CC2 because the original caption decoders only read the first odd field, but later switched to using CC3 for bandwidth reasons. Due to the same bandwidth reasons XDS was never used by Spanish-speaking stations.

Within each channel, there are two streams of information which might be considered sub-channels: one carries "captions" and the other "text." The latter is not in common use due to the lack of hardware support and bandwidth available. Text is signaled by the use of text commands and can be used for a formatted URL string with a 16-bit checksum that designates a web site that the captions relate to or a local station communication channel.

This layering is based on the OSI Protocol Reference Model:

OSI Layers CC Layers DVB/MXF Layers Comments
Application Interpretation Issuing commands and appending text to rows
Presentation Coding Breaking up individual commands and characters
Session Channel Channel Byte Stream
-- Selection CC channel assembly from CC byte pairs
Transport Injection Synchronization CC byte pairs extracted/synchronized with/from video frames
Network unused directly connected link
Link SMPTE 259M or H.222 or MXF video frames or VBI data split from link format
Physical SDI or DVD ODFM or
storage medium
link format demodulated/retrieved from transmission/source

DVD GOP User Data Insertion[edit]

The user data structure that follows a H.262 GOP header is as follows (the same would apply after an ISO/IEC 14496-2 GOP header):

Length Name Type Default
32 bits user_data_start_code patterned bslbf 0x000001B2
16 bits user_identifier ASCII bslbf CC
8 bits user_data_type_code uimsbf 1
8 bits caption_block_size inverted uimsbf 0xf8
1 bit caption_odd_field_first flag 1
1 bit caption_filler alignment 0
5 bits caption_block_count uimsbf 15
1 bit caption_extra_field_added flag 0
X*24 bits caption_block binary free form

bslbf: bit string, left bit first ; uimsbf: unsigned integer, most significant bit first

Caption blocks are inserted after the sequence and GOP headers, so each block is for one second of video which would end up being one or two long lines or three to four short lines of text. Also that means if the caption_block_count is greater than 30 then the block contains both interleaved caption fields and one could devise the framing rate from the caption_block_count. However since the data is grouped together the framing rate will almost always be 30/1.001, unlike the ATSC method that inserts one byte pair for each field after the picture header making framing rates of 24/1.001 possible for HD content. Since when a decoder does a 3:2 pull-down for NTSC output the captions will remain in sync.

DVD Caption Block
Length Name Type Default
7 bits caption_filler alignment 0x7f
1 bit caption_odd_field uimsbf 1 or 0
8 bits caption_first_byte odd parity uimsbf 0x80
8 bits caption_second_byte odd parity uimsbf 0x80

DVB Transport Insertion[edit]

The packet-ed structure that is inserted before the H.222 video packet is as follows for a frame of associated video:

Length Name Type Default
32 bits private_stream_1_start_code patterned bslbf 0x000001BD
16 bits PES_packet_length uimsbf 176
2 bits PES_version uimsbf 2
1 bit PES_priority flag 0
2 bits PES_scrambling_control uimsbf 0
1 bit data_alignment_indicator flag 1
2 bits copyright
original
uimsbf 0
2 bits PTS_DTS_flag uimsbf 2
6 bits various_PES_flags uimsbf 0
8 bits PES_header_data_length uimsbf 36
40 bits PTS uimsbf varies
248 bits stuffing_bytes uimsbf 255
8 bits data_identifier uimsbf 153
8 bits data_unit_id uimsbf 197
8 bits data_unit_length uimsbf 3
2 bits reserved_future_use uimsbf 3
1 bit field_parity (CC1/2) flag 0
5 bits line_offset uimsbf 21
16 bits closed_captioning_data_block uimsbf 608 caption
8 bits data_unit_id uimsbf 197
8 bits data_unit_length uimsbf 3
2 bits reserved_future_use uimsbf 3
1 bit field_parity (CC3/4/XDS) flag 1
5 bits line_offset uimsbf 21
16 bits closed_captioning_data_block uimsbf 608 caption
8 bits data_unit_id uimsbf 255
8 bits data_unit_length uimsbf 124
124*8 bits stuffing_bytes uimsbf 255

bslbf: bit string, left bit first ; uimsbf: unsigned integer, most significant bit first

This structure was designed for any digital VBI data and was optimized to carry three or more 43-byte Teletext packets. e.g. a page header and two associated lines. For Teletext subtitles, the data_unit_id is set to 3. In this form, captions have to be separated into byte pairs spread over frames in one second of video rather than grouped into one block as with the DVD structure. The same is true for Teletext subtitles with more than one line of text.

SDI/MXF SMPTE 291M Insertion[edit]

The packet-ed structure that is inserted before the SMPTE 259M active video frame or MXF essence video packet is coded as follows for a frame of associated video:

Length Name Type Default
16 or 128 bits ancillary_flag or
ancillary_header
patterned bslbf or
7 uimsbf
0xFFFF or
varies
8 bits data_id uimsbf 97
8 bits secondary_data_id uimsbf 2
8 bits data_count uimsbf varies
X*24 bits caption_data_block binary free form

bslbf: bit string, left bit first ; uimsbf: unsigned integer, most significant bit first

This structure was designed for any digital audio or metadata that is to be synchronized with a video frame. SDI transports every eight bits in a 10 bit aligned packet, unlike MXF which is byte aligned and the ancillary flag bytes are replaced by 128 bit header.

SDI/MXF Caption Block
Length Name Type Default
1 bit caption_odd_field
(CC1/2 = 1; CC3/4 = 0)
flag 1
2 bits caption_reserved uimsbf 0
5 bits caption_line_offset uimsbf 15
8 bits caption_first_byte odd parity uimsbf 0x80
8 bits caption_second_byte odd parity uimsbf 0x80

Extended Data Service[edit]

The EIA-608 data stream format includes Extended Data Service (XDS), a variety of information about the transmission. It is all optional, and can include:

  • channel name
  • channel call letters
  • program name
  • offensiveness rating (violence, sex, etc.)
  • program category (drama, game show, etc.)

Characters[edit]

There are three sets of characters that the EIA-608 stream can direct the receiver to display: basic characters, special characters, and extended characters. A single two-byte EIA-608 command (represented by a single VBI line) can specify two basic characters, one special character, or one extended character.

Extended characters are a later addition to the standard and their decoding is optional.

EIA-608 provides controls for the color of the foreground and background of the text, underlining, blinking, and italics. The default color scheme is white characters on a black background, all opaque.

The Transparent Space special character implies a transparent background even in the absence of any background control commands. As the foreground of this character is a blank space, it really means a gap in the close caption text.

Non-Caption Data[edit]

This is used to either pad out the field line when no captions are sent or for the eXtended Data Service.

          +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+              +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 null pad |P|0|0|0|0|0|0|0| |P|0|0|0|0|0|0|0| XDS metadata |P|0|0|0| CLASS | |P|0|0|0|  TYPE | 
          +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+              +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
          15             8   7             0               15             8   7             0

Basic North American character set[edit]

A command with bits 13 or 14 on directs the receiver to display two basic characters at the current cursor position for the current mode (closed caption or text). Each character is a code point (identifies the character to display), as follows.

                       +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
  modified 7-bit ASCII |P|  CHARACTER1 | |P|  CHARACTER2 |
                       +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
                       15             8   7             0

The code is almost identical to ASCII; the exceptions are shown in red.

Binary Decimal Hex Glyph
0010 0000 32 20 (SP)
0010 0001 33 21 !
0010 0010 34 22 "
0010 0011 35 23 #
0010 0100 36 24 $
0010 0101 37 25 %
0010 0110 38 26 &
0010 0111 39 27
0010 1000 40 28 (
0010 1001 41 29 )
0010 1010 42 2A á
0010 1011 43 2B +
0010 1100 44 2C ,
0010 1101 45 2D -
0010 1110 46 2E .
0010 1111 47 2F /
0011 0000 48 30 0
0011 0001 49 31 1
0011 0010 50 32 2
0011 0011 51 33 3
0011 0100 52 34 4
0011 0101 53 35 5
0011 0110 54 36 6
0011 0111 55 37 7
0011 1000 56 38 8
0011 1001 57 39 9
0011 1010 58 3A :
0011 1011 59 3B ;
0011 1100 60 3C <
0011 1101 61 3D =
0011 1110 62 3E >
0011 1111 63 3F ?
 
Binary Decimal Hex Glyph
0100 0000 64 40 @
0100 0001 65 41 A
0100 0010 66 42 B
0100 0011 67 43 C
0100 0100 68 44 D
0100 0101 69 45 E
0100 0110 70 46 F
0100 0111 71 47 G
0100 1000 72 48 H
0100 1001 73 49 I
0100 1010 74 4A J
0100 1011 75 4B K
0100 1100 76 4C L
0100 1101 77 4D M
0100 1110 78 4E N
0100 1111 79 4F O
0101 0000 80 50 P
0101 0001 81 51 Q
0101 0010 82 52 R
0101 0011 83 53 S
0101 0100 84 54 T
0101 0101 85 55 U
0101 0110 86 56 V
0101 0111 87 57 W
0101 1000 88 58 X
0101 1001 89 59 Y
0101 1010 90 5A Z
0101 1011 91 5B [
0101 1100 92 5C é
0101 1101 93 5D ]
0101 1110 94 5E í
0101 1111 95 5F ó
 
Binary Decimal Hex Glyph
0110 0000 96 60 ú
0110 0001 97 61 a
0110 0010 98 62 b
0110 0011 99 63 c
0110 0100 100 64 d
0110 0101 101 65 e
0110 0110 102 66 f
0110 0111 103 67 g
0110 1000 104 68 h
0110 1001 105 69 i
0110 1010 106 6A j
0110 1011 107 6B k
0110 1100 108 6C l
0110 1101 109 6D m
0110 1110 110 6E n
0110 1111 111 6F o
0111 0000 112 70 p
0111 0001 113 71 q
0111 0010 114 72 r
0111 0011 115 73 s
0111 0100 116 74 t
0111 0101 117 75 u
0111 0110 118 76 v
0111 0111 119 77 w
0111 1000 120 78 x
0111 1001 121 79 y
0111 1010 122 7A z
0111 1011 123 7B ç
0111 1100 124 7C ÷
0111 1101 125 7D Ñ
0111 1110 126 7E ñ
0111 1111 127 7F SB

In the table above, SB represents a solid block. The apostrophe (code 27), which may originally have been intended to be a neutral apostrophe as in ASCII, is now recommended to be rendered as a right single quotation mark (Unicode U+2019). For a neutral single quote/apostrophe, the plain single quote from the extended character set should be used.[2]

Special North American character set[edit]

The only real use in North America of this set is the use of the Eighth note character to denote changes from spoken dialogue to singing or musical only scenes.

It is an acceptable broadcast engineering practice when translating EIA-608 to Teletext for PAL compatible countries to substitute this character for a number sign because of its similarity to a sharp.

A command to display a special character has a first byte of 0x11 or 0x19 (depending upon channel). The second byte is a code point in the range 0x30-0x3F as follows.

 +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 |P|0|0|1|C|0|0|1| |P|0|1|1|  CHAR |
 +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 15             8   7             0
 P = odd parity ; C = second channel toggle
Binary Decimal Hex Glyph
0011 0000 48 30 ®
0011 0001 49 31 °
0011 0010 50 32 ½
0011 0011 51 33 ¿
0011 0100 52 34
0011 0101 53 35 ¢
0011 0110 54 36 £
0011 0111 55 37
0011 1000 56 38 à
0011 1001 57 39 TS
0011 1010 58 3A è
0011 1011 59 3B â
0011 1100 60 3C ê
0011 1101 61 3D î
0011 1110 62 3E ô
0011 1111 63 3F û

TM is short for unregistered trademark and should be represented in superscript (™). TS in the table above represents a "transparent space" or non-breaking space. Finally, the Eighth note (♪) is used to denote singing or background music in captions.

Extended Western European character set[edit]

 +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 |P|0|0|1|C|0|1|S| |P|0|1|CHARACTER|
 +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 15             8   7             0
 P = odd parity ; C = second channel toggle ; S = char set toggle

These extended character sets are rarely used due to most European countries using the BBC Ceefax based Teletext system.

The Ceefax system is more prone to character errors due to the greater number of data bits (337 versus 16) encoded per VBI field, these errors occur either on noise prone analog transmissions or connections.

  • A command to display an extended Spanish/French or miscellaneous character has a first byte of 0x12 or 0x1A (depending upon channel).
  • A command to display an extended Portuguese/German/Danish character has a first byte of 0x13 or 0x1B (depending upon channel).

The second byte is a code point in the range 0x20-0x3F is as follows

Extended Spanish/Miscellaneous
Binary Decimal Hex Glyph
0010 0000 32 20 Á
0010 0001 33 21 É
0010 0010 34 22 Ó
0010 0011 35 23 Ú
0010 0100 36 24 Ü
0010 0101 37 25 ü
0010 0110 38 26 ´
0010 0111 39 27 ¡
0010 1000 40 28 *
0010 1001 41 29 '
0010 1010 42 2A -
0010 1011 43 2B ©
0010 1100 44 2C SM
0010 1101 45 2D ·
0010 1110 46 2E "
0010 1111 47 2F "
  Extended French
Binary Decimal Hex Glyph
0011 0000 48 30 À
0010 0001 49 31 Â
0011 0010 50 32 Ç
0011 0011 51 33 È
0011 0100 52 34 Ê
0011 0101 53 35 Ë
0011 0110 54 36 ë
0011 0111 55 37 Î
0011 1000 56 38 Ï
0011 1001 57 39 ï
0011 1010 58 3A Ô
0011 1011 59 3B Ù
0011 1100 60 3C ù
0011 1101 61 3D Û
0011 1110 62 3E «
0011 1111 63 3F »
  Portuguese
Binary Decimal Hex Glyph
0010 0000 32 20 Ã
0010 0001 33 21 ã
0010 0010 34 22 Í
0010 0011 35 23 Ì
0010 0100 36 24 ì
0010 0101 37 25 Ò
0010 0110 38 26 ò
0010 0111 39 27 Õ
0010 1000 40 28 õ
0010 1001 41 29 {
0010 1010 42 2A }
0010 1011 43 2B \
0010 1100 44 2C ^
0010 1101 45 2D _
0010 1110 46 2E |
0010 1111 47 2F ~
  German/Danish
Binary Decimal Hex Glyph
0011 0000 48 30 Ä
0010 0001 49 31 ä
0011 0010 50 32 Ö
0011 0011 51 33 ö
0011 0100 52 34 ß
0011 0101 53 35 ¥
0011 0110 54 36 ¤
0011 0111 55 37 ¦
0011 1000 56 38 Å
0011 1001 57 39 å
0011 1010 58 3A Ø
0011 1011 59 3B ø
0011 1100 60 3C +
0011 1101 61 3D +
0011 1110 62 3E +
0011 1111 63 3F +

SM is short for service mark and should be represented in superscript. The single quote mark is a curly left and double quote marks are curly left and right. The plus signs refer to top left, top right, lower left and lower right corners for box drawing.

Non-Western Norpak Character Sets[edit]

When used all standard and extended character sets are unused in favor of the following predefined sets, care must be taken to not emulate any control commands. This is an extension submitted to the CEC by Norpak who made a similar extension to the Teletext format for the Chinese market. The main use has been to provide double byte code point captioning to the Japanese, Taiwanese and South Korean markets. A command to switch character sets has a first byte of 0x17 or 0x1F (depending upon channel). The second byte is a character set reference in the range 0x24-0x2A as follows

 +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 |P|0|0|1|C|1|1|1| |P|0|1|0|CHARSET|
 +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 15             8   7             0
Binary Decimal Hex Set in Use
0010 0100 36 24 Standard
0010 0101 37 25 Standard Double Height
0010 0110 38 26 Decoder Specific 1
0010 0111 39 27 Decoder Specific 2
0010 1000 40 28 China's GB 2312 (1980)
0010 1001 41 29 Korea's KS C 5601 (1987)
0010 1010 42 2A Loadable

Control commands[edit]

Bits 15 and 7 are always odd parity bits. Bit 11 is always the channel bit.

For a preamble address code these are as follows: Bits 15 and 7 are parity bits. Bits 14 and 13 are always 0, bits 12 and 6 are always 1. Bits 10, 9, 8 and 5 indicate the row position. Bits 4, 3, 2 and 1 indicate the attribute of the text. Bit 0 indicates underline.

Row Preamble Standard Address and Style
(Default Row 11 = 0,top rows 1-4 = 1-2,bottom rows 12-13 = 3)
                +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+                  +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 preamble style |P|0|0|1|C|0|ROW| |P|1|N|0|STYLE|U| preamble address |P|0|0|1|C|0|ROW| |P|1|N|1|CURSR|U|
                +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+                  +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
                15             8   7             0                   15             8   7             0
Row Preamble Extended Address and Style
(Bottom Rows 14-15 = 0,middle rows = 5-10 = 1-3)
                +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+                  +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 preamble style |P|0|0|1|C|1|ROW| |P|1|N|0|STYLE|U| preamble address |P|0|0|1|C|1|ROW| |P|1|N|1|CURSR|U|
                +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+                  +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
                15             8   7             0                   15             8   7             0
 P = odd parity ; C = second channel toggle
 U = underline toggle ; N = next row down toggle
 (if style or cursor position not set,
  defaults are regular white text with black background
  at cursor = 0, cursor - multiple of 4)
 text style enumerations:
  {white=0,green,blue,cyan,red,yellow,magenta,italic white}

The row bits specify which of the fifteen screen rows should contain the caption text: row 11 (0000), 1 (0010), 2 (0011), 3, 4, 12, 13, 14, 15, 5, 6, 7, 8, 9, or 10 (1111).

The attributes bits allow 16 possibilities, which are: white (0000), green, blue, cyan, red, yellow, magenta, italics, indent 0, indent 4, indent 8, indent 12, indent 16, indent 20, indent 24, indent 28 (1111).

For a midrow code these are as follows: Bits 14, 13, 10, 9, 6 and 4 are always 0, bits 12, 8 and 5 are always 1. Bits 3, 2 and 1 form the color attribute (see the listing of attributes). Bit 0 indicates underline.

Mid Row Style Change
(style remains in effect until either next change or end of row signaled by a control or preamble)
           +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+              +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
  bg color |P|0|0|1|C|0|0|0| |P|0|1|0|COLOR|T| midrow style |P|0|0|1|C|0|0|1| |P|0|1|0|STYLE|U|
           +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+              +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
           15             8   7             0               15             8   7             0
       +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+            +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
 no bg |P|0|0|1|C|1|1|1| |P|0|1|0|1|1|0|1| black text |P|0|0|1|C|1|1|1| |P|0|1|0|1|1|1|U|
       +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+            +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
       15             8   7             0             15             8   7             0
 P = odd parity ; C = second channel toggle
 T = partially transparent ; U = underline toggle
 bg color enumerations:
 {white=0,green,blue,cyan,red,yellow,magenta,black}

For other control codes these are as follows: Bits 14, 13, 9, 6 and 4 are always 0, bits 12, 10 and 5 are always 1. Bit 8 chooses between line 21 and 284. Bits 3, 2, 1 and 0 identify the particular action.

The command bits allow 16 possibilities, which are: resume caption loading (0000), backspace (0001), delete to end of row (0100), roll-up captions 2-rows, roll-up captions 3 rows, roll-up captions 4-rows, flash on (0.25 seconds once per second), resume direct captioning, text restart, resume text display, erase displayed memory, carriage return, erase nondisplayed memory, end of caption (1111).

For tabs these are as follows: Bits 14, 13, 6, 4, 3, 2 are always 0, bits 12, 10, 9, 8, 5 are always 1. Bits 1 and 0 determine the number of tab offsets.

References[edit]

  1. ^ "SCTE 21 2012 - STANDARD FOR CARRIAGE OF VBI DATA IN CABLE DIGITAL TRANSPORT STREAMS". Society of Cable Telecommunications Engineers. SCTE 21: 13. 2012. Retrieved 4 October 2012. 
  2. ^ CEA-608-E R-2014 standard

External links[edit]