Teletext Recovery Editor Documentation
Overview
The Teletext Recovery Editor (TRE) is designed to aid with repairing recovered teletext services. Users can see all of the pages in a service at a glance, click on a carousel, see its subpages, select a subpage and edit it. The corrected subpage can then be saved back into the source file.
It can also recombine separate carousels into a single T42 file for upload to The Teletext Archive.
An experimental feature is present where the fixed carousels can be applied to a copy of the original, as broadcast T42, which keeps the original timings of the service for use in the Teletext Player for the most authentic teletext experience.
Basic Operation
The TRE expects a folder containing carousel files (a carousel is a page which consists of one or more subpages). You provide it with a folder, and TRE will scan the folder to show its contents (which should be lots of small t42 files, not a single large one).
To create such a folder (called a ‘binaries’ folder for reasons which are unlikely to become clear for the time being), use vhs-teletext to split a squashed T42 file:
teletext split <path>\binaries\{m}{p}.bin <path to squashed t42 file>
When the folder that the above command creates is dropped onto TRE, something like this will be displayed:
On the right is a list of the pages present in the service. If one is clicked, the subpages are shown in the pane to the right:
Then, when a subpage is clicked, the subpage opens for editing on the right-most pane:
The page can now be edited to correct errors as a result of recovery from tape. Once done, the menu item Carousel->Save Carousel will save all of the subpages back into their carousel file.
If you move to another carousel, TRE will ask if the page should be saved before moving, as otherwise moving will lose the changes made.
A page can be exported to PNG format for sharing on social media etc. using Page->Export Currently Selected Page…->PNG.
Editor
The editor works in overwrite mode, i.e. typed characters overwrite the one currently under the cursor. This means that the backspace key clears the character under the cursor with a space character, and the insert key moves the text after the cursor to the right and inserts a space character.
When editing a page, the following shortcut keys are available:
CTRL-C
You can use the mouse to select part of a line or a box on the teletext page. CTRL-C copies this to the clipboard.
When no text is selected, the character under the cursor is copied. This is useful for copying control codes.
CTRL-L
Copies the entire line under the cursor to the clipboard. Useful for copying a known good graphic line from one subpage to another.
CTRL-V
Pastes the clipboard contents into the editor. If this goes off-screen then the off-screen portions will be discarded.
CTRL-Z
Undo the last change. This doesn’t work correctly yet, do not use it.
Changing text/graphics modes and colours
The following shortcut keys set the mode to text and the appropriate colour:
Black : CTRL-K
Red : CTRL-R
Green : CTRL-G
Yellow : CTRL-Y
Blue : CTRL-B
Magenta : CTRL-M
Cyan : CTRL-S
White : CTRL-W
Graphics codes are the same as the above, but with holding SHIFT as well as CTRL.
CTRL-cursor up
Edits the previous page in the recovered files list, e.g. if you are on page 401 the editor would move to 400.
CTRL-cursor down
Edits the next page down in the recovered files list.
Menu Options
Service Menu
This menu performs actions to the whole service (or collection of carousels)
Service->Open Binaries Folder…
Opens a folder containing carousel files. The same as dropping a folder onto the TRE.
Service->Create Teletext Stream…
Not in use.
Service->Trim and Combine Carousels to T42…
Attempts to remove any duplicate subpages which are copies of another page but containing blank lines, and outputs a single T42 file for upload to the Teletext Archive or for viewing in the Teletext Player.
Service–>Merge Binaries into a T42…
Attempts to take the binaries folder, containing repaired t42 carousel files, and place them back into the original, unsquashed recovered T42 file from vhs-teletext. This has the effect of cleaning up the as-broadcast service so that it can be experienced as-broadcast in Teletext Player. This is explained in more detail later.
Service–>Search
Not in use.
Service–>About
Update history etc.
Carousel Menu
This menu controls actions performed on a carousel (group of sub pages) level.
Carousel->Open Carousel…
Opens a carousel file independently of the Recovered Pages list.
Carousel->Save Carousel
Saves the current carousel over its source file.
Carousel->Save Carousel As…
Saves the current carousel to another file
Carousel–>Export Carousel
When given a folder, this option saves all of the subpages to individual files in the chosen format (only PNG for now)
Carousel–>Clear Carousel…
Clears the contents of the carousel back to one subpage template. This does not write to disk until you save.
Page Menu
Page–>Import base64Url Link…
Opens a text box where base64Url data can be pasted for import into the current editor window.
Online editors such as edit.tf and ZXGuesser’s editor store the page data in the page URL. These data look like a long string of random alphanumerical characters. This feature allows you to paste the URL into the text box, and the program will decode the URL data back into teletext data and overwrite the current contents of the editor window.
Page–>Export Currently Selected Page
This allows the export of the currently selected page to another format. “Currently selected” means that the thumbnail must be highlighted – otherwise a pop-up window will advise of this.
PNG
A standard, non-lossy compressed format, which retains the colours and position of every pixel. Ideal for sharing on the web. Binary data.
TTI
A text based standard from MRG Systems. Can be opened in a text editor for human eyes.
EP1
A file format introduced with Softel’s teletext editor Flair. Only really used for interoperability with that program.
edit.tf
Not implemented – intended to provide a base64Url format as described above.
C64 Teletext Reader
Not completed. The intention was to be able the save pages in a format for viewing on the C64 Teletext Reader (https://norbertkehrer.github.io/teletext_c64.html)
Preferences Menu
Preferences–>Presentation Level…
Level 1 teletext is the basic specification, as launched in September 1976. All teletext sets understand this mode. Level 1.5 adds more national options characters than the few available under Level 1 and some other enhanced features.
Most teletext services are Level 1.5. Some teletext providers, mostly in mainland Europe, provided enhancements at Level 2.5 – to check, simply switch the presentation level to 2.5 – if there are any extra features available they will be displayed, but if not the Level 1.5 page will continue to be displayed as fallback.
Not all Level 2.5 features are yet supported in Teletext Recovery Editor.
More on Presentation Levels
In its early days, before the teletext standard was set as Level 1 in September 1976, the code table (a 32-byte list of teletext attributes, such as text colours, graphics colours and toggles such as flash on/off) did not contain all of the features that users are accustomed to. On a technical level, some of the codes were shifted around in the code table over time.
The upshot of this is that early teletext recoveries will not display properly if viewed using a decoder which only understands Level 1 upwards. Teletext Recovery Editor can display these as intended: in the Presentation Levels menu, these pre-spec. standards are labelled by their date (until 1/9/1975, and 1/1/1976). There may well be others as yet undiscovered.
A teletext page consists of 24 lines (25 including Fastext) for display. The teletext standard has room for 32 lines – the remaining 7 (i.e. lines, or packets 25-31) cannot be seen on a regular teletext display, but can still be transmitted and recieved by a special decoder.
These additional packets are used for some enhanced features in Level 1.5 (the enhanced features give the level the extra 0.5!) and the vastly-expanded feature sets in Levels 2.5 and 3.5.
In the menu there is Level 2 – (as distinct from Level 2.5) – this is the same as Level 2.5 but the colour palette is different. Level 2 was used by BBC Ceefax for its experimental in-vision Level 2 pages in the mid-90s.
Level 4 is alphageometric teletext. It supports high resolution graphics by way of being able to draw lines, circles, arcs and filling enclosed areas.
Preferences–> Character Set…
The Editor contains character sets from several teletext decoder chips that were manufactured over the years.
The default is Mullard, named for the manufacturer who made the chip in the BBC Micro’s Mode 7 and many teletext sets in the 80s.
ETS is the character set of the 90s, which is an implementation of the character set detailed in the European Broadcasting Union’s Enhanced Teletext Specification. Modern teletext pages should be viewed using this set as it contains all of the Level 2.5 extended character set.
TiFax is the character set used in Texas Instruments decoders, popular in the late 70s and early 80s. Notably used for Ceefax In Vision during this period.
“1975 Generic ASCII” is manually drawn from the BBC feature This is Ceefax. It was used in teletext’s early days, and pre-1976 pages are best rendered using this. A few glyphs change the appearance of contemporary artwork.
Preferences–>National Option Sets
The implemention of the teletext standard is a little inconsistent over some services, so this feature gives the option of forcing the decoder to display characters from a particular national set. Not all national sets are present – they are being implemented on an as-and-when basis.
Preferences–>Show Borders
Teletext sets displayed teletext pages with large borders in the background colour. This feature gives the option to display these or not, for extra authenticity.