This archive contains 2 types of teletext archives.

t42 files are a popular format with packets of 42 octets. Theese octets essentially contain a teletext packet each.

tta files are like t42 files. However there's a 4096 octet header in front of them. If you chop it off you get a normal t42 file. Pages are stored in order including the subpages.
The header has 0x7ff entries each containing the number of teletext packets per page (including subpages). This allows for speedy seeking.