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ali1234 / vhs-teletext

Software to recover teletext data from VHS recordings.
GNU General Public License v3.0
179 stars 21 forks source link

Implement parsing for the rest of the packets #36

Open ali1234 opened 4 years ago

ali1234 commented 4 years ago

Reading:

Writing:

Blocks #35

ali1234 commented 4 years ago

@ZXGuesser I pulled your checksum patch. What do we need to do for the others?

ZXGuesser commented 4 years ago

26, and 28 need hamming 24/18 decoding into the thirteen 18-bit "triplets" in addition to the designation code which is already done to be able to squash them in subpages. I did that with the classic XOR algorithm last time, but there's a fast look-up table based method. X/29 can be decoded the same to weed out the errors, but being non page-related like packet 8/30 it's not something that gets squashed yet.

X/30 and X/31 are again not related to pages at all, and aren't squashable data. The packets should be one the standard databroadcast formats, but the payload of the datastreams could be anything and some are encrypted. I would just pass the raw packets through for "later analysis" at least for the time being.

Not sure what you'd want to do for parsing the enhancement packets in terms of the debug output. There's a lot of stuff none of which is really human readable, so maybe just display the error counts.