EIA-608

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EIA-608, also known as line 21 captions, is the standard for closed captioning for NTSC TV broadcasts in the United States and Canada. It was developed by the Electronic Industries Alliance.

EIA-608 captions are transmitted in the vertical blanking interval in NTSC broadcasts, and are also sometimes present in the picture user data in ATSC transmissions. It uses a fixed bandwidth of 960 bit/s.

EIA-608 is being phased out with the transition to digital television. ATSC broadcasts support EIA-708 captions, which include full support for Spanish and French, and nearly-complete support for other Western European languages.

Characters in EIA-608 are encoded either with single or double byte characters. The single byte characters closely resemble ASCII. In the table below exceptions from the ASCII standard are shown in red. Except for the transparent space (TS) all characters should be written as white characters on a black background. The top bit in each byte is an odd-parity bit.

[edit] Single-byte characters

Binary Decimal Hex Graphic 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 Graphic 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 Graphic 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.

[edit] Double-byte characters

Double byte characters are preceded by an escape character, 0x11.

Binary Decimal Hex Graphic 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 MN 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, MN should be a musical note (♪), which is used to denote singing in captions.

[edit] Control characters

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.

The row bits specify which of the 15 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.

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 form a command.

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.