On Tue, 27 Jan 2009, Daniel Dalton wrote:
[Now, ideally, a teletext service, being text-based, can be]> > trivially converted to braille or spoken. I'm not sure about> > Braille..., what format do they originate in? Is it tv signal, or some> kind of text guide or something?
The teletext service I hope you would be able to get, is sentas part of the digital service. Here I will quickly explainthat a Transport Stream, which is used by DVB-T, mixes togetherdigital versions of several services, including audio soundtrack,or radio, as well as video signals, and additional data services,with each component being able to be identified by its own ID.
A conventional set-top-box will convert the video from itsdigital form to an analogue equivalent, then convert the audiosoundtrack into its analogue form, and decode and add theteletext to the video signal, perhaps also including its owninternal teletext decoder for user convenience.
Then these analogue signals are delivered to your tv by one ofmany means, be it as an RGB signal through a SCART connector,or in the worst case, by modulating an RF carrier.
But your Linux machine will be working with the TransportStream directly, selecting the particular IDs of interest.When you look at that particular ID, you see merely adatastream including the payload.
So, just as your TV audio will be carried in a form whichwill be similar to the mp3 files you've certainly used, orwhatever format, you can also write the teletext data toa file and work with that.
When you get your tuner working, or one that does, if youdo receive a teletext service, I'll guide you through thesteps needed to actually see the content being broadcast.
As a little teaser, I will paste part of a hexdump of anupdate to today's rates of the example I posted earlier.
000001c0 20 20 20 20 20 cb 61 6e 61 64 61 ae ae ae ae 20 | .anada.... |000001d0 a8 43 c1 c4 29 83 20 20 31 2c b6 31 38 37 02 20 |.C..). 1,.187. |000001e0 ab b0 2c b3 37 25 07 31 32 ba b0 37 20 d3 fd 64 |..,.7%.12..7 ..d|000001f0 61 e6 f2 e9 6b 61 ae 20 a8 da c1 52 29 83 20 31 |a...ka. ...R). 1|00000200 b3 2c b3 37 b6 31 02 20 ab b0 2c b5 b6 25 07 31 |.,.7.1. ..,..%.1|00000210 31 ba b5 b0 20 c8 ef 6e 67 6b ef 6e 67 ae ae 20 |1... ..ngk.ng.. |00000220 a8 c8 cb c4 29 83 20 31 b0 2c 32 b5 b6 37 02 20 |....). 1.,2..7. |00000230 ab b0 2c 31 b6 25 07 31 31 ba 34 b9 20 d3 e9 6e |..,1.%.11.4. ..n|
There are some readable parts of words (Canada, Hongkong)to be seen in the ASCII dump at the right, but it is notquite a simple text dump.
The program I hacked to display this in text form doesthe conversion into ASCII with the added characters forthe particular language in use.
So, to answer your question, essentially it is a textguide.
Now, the MHEG service, in contrast, is Java based, and Ihave downloaded a good number of files, both text andbinary, that would be used to display a particular page.However, I can't see a simple way to get at the textinfo within and display it. That would be for someonewho has studied and understands this service.
> Thanks, that looks interesting, so does it all depend on what service is> available here in Australia?
That is correct. One more thing I should note, is thatthis text type of teletext supports, and broadcastersgenerally make heavy use of, features such as colours,double-height and blinking characters, and in particular,parts of character blocks that can be used to createsimple graphics. Think of some sort of ASCII art, or,with the most common use made of these graphics bycommercial broadcasters, ASCII pr0n.
DANGER! ASCII PR0N PASTED BELOW! SENSITIVE READERSSHOULD AVERT THEIR GAZE OR SKIP TO THE NEXT MESSAGE!^LI MEAN IT! IT COULD QUALIFY AS EXTREME PORN!^LTHAT'S IT, I TAKE NO RESPONSIBILITY FOR YOUR ACTIONS!
This pr0n is made worse by the fact that my console fontdoes not include the full range of teletext partial blocks,so I've substituted characters such as `*' and `X' to tryand give a feel for how the graphics should appear.Maybe a full Unicode X font will include such charactersand I can simply map them to UTF8, but I'm primarilyinterested in the text content information on my text console.
Here's the pr0n...
█X█X*XX*???*?██ XXX* AMI █X?█??*█ █X?* █ **XXXX
No, this is not going to work. There are too many characterswhich are not yet converted to something and I'm having to addas `?' by hand. Anyway, the blocks on the left are used toform words; to the right the blocks would be forming the topof a female head.
auszuziehen.Magst *X*███XX*██ Du mir die Kleider *XX████X* ██ vom Leib reissen? XX██████* X█*
At the right, part of a stomach and arm
Well, anyway, if these non-ASCII full blocks have made itthrough intact and are diplaying correctly anywhere, thatis an example of the crude (in more than one sense of theword) images one can make from the text medium of teletext.
And as far as colour -- the background would be black,with the blocks-forming-letters as well as the text yellow,and the female image formed from red partial blocks.
Ah, another UTF8 project for me to add to my list...
barry bouwsma
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