Channels
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. The channels are often presented to users numbered simply as CC1-2 for the odd field and CC3-4 for the even field. 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.0 This layering is based on the OSI Protocol Reference Model:DVD GOP User Data Insertion
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): 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.DVB Transport Insertion
The packet-ed structure that is inserted before theSDI/MXF SMPTE 291M Insertion
The packet-ed structure that is inserted before theExtended Data Service
The EIA-608 data stream format includes Extended Data Service (XDS), a variety of information about the transmission. It is all optional,: * * * program name * offensiveness rating (violence, sex, etc.) * program category (drama, game show, etc.)Characters
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
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
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 0The code is almost identical to ASCII; the exceptions are shown in red. 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.CEA-608-E R-2014 standard
Special North American character set
The only typical use in North America of this set is the use of the+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ , P, 0, 0, 1, C, 0, 0, 1, , P, 0, 1, 1, CHAR , +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ 15 8 7 0 P = odd parity ; C = second channel toggleTM is short for unregistered trademark and should be represented in superscript (™). TS in the table above represents a "transparent space" or
Extended Western European character set
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ , 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 toggleThese 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 SM is short for
Non-Western Norpak Character Sets
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+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ , P, 0, 0, 1, C, 1, 1, 1, , P, 0, 1, 0, CHARSET, +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ 15 8 7 0
Control commands
Bits 15 and 7 are always odd parity bits. Bit 11 is always the channel bit. Preamble address code with masking bit 15,11 and 7 as already defined above can be interpreted from following tableRow 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: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 0001X10X(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: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. Considering parity bit already ignored hex value have of 2 byte data is following command:
References
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