Talk:EIA-608
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This article is hard to follow, even for me, and I already (roughly) know how line 21 subtitles work!
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Part of the difficulty is that there are subtle errors in the article, and part of it is that the presentation is chaotic and doesn't start with a broad overview.
And it is so simple at its core. Line 21 of the vertical blanking interval contains a black line with a series of grey pulses like this:
| detect & sync signature | char 1 . | P | char 2 . | P | _ _ _ _ _ _ _ ___ ___ _______ ___ ___ ___
So two characters, or one 14-bit control code, can be transmitted per line, in this case 0000101 (= P) and 0100101 (= R). The bits are transmitted from least significant to most and P is set so the parity is odd (an odd number of ones).
Every new frame two more characters can be sent. Here's an actual example:
- ... 0000000 0000000 0010100-0000010(×2) 0010100-0100101(×2) PROVIDED YOU COULD 0010100-0100111(×2) BL ...
The codes marked with ×2 are sent twice because they're control codes and their corruption would have more severe effects than the corruption of a character.
The 0000000 codes are empty padding padding characters and are continuously sent when there's no subtitle data to be sent.
0010100-0000010 is a control code (..1.100 ....010) with data: field=0 extended=false channel=0 / control=0000 (= resume caption loading)
0010100-0100101 is a row preamble (....100 ....1.1) with data: row=001 (= 14/15) channel=0 / underline=false indent=100 (= 4) nextrow=false (so: 14).
0010100-0100111 is also a row preamble with data: row=001 (= 14/15) channel=0 / underline=false indent=100 (= 4) nextrow=true (so: 15).
Control codes follow the pattern aaac(hannel)100-xxxxbbb as in the following table:
bbb \ aaa: 000 100 010 110 001 101 011 111 010 MR bg MR style xchar xchar ctl f0 ctl f1 text n/p xctl 110 schar --- xchar xchar --- --- text ne/c/e --- 001 RP style row= 11 1 3 12 14 5 7 9 101 RP cursor " 11 1 3 12 14 5 7 9 011 RP style " (12) 2 4 13 15 6 8 10 111 RP cursor " (12) 2 4 13 15 6 8 10
And codes with the pattern xxxx000-xxxxxxx are for XDS.
This isn't as difficult as the article pretends it is by a far stretch. (Why'd they have to mix up the rows though?) — Preceding unsigned comment added by 80.114.146.117 (talk) 13:45, 29 December 2016 (UTC)