a big HI with bugs and wishes

[Chris]

No no, it's not that! I am surprised it's transmitted on DVB. I'm at a loss as to how it is done, or how any of this stuff *could* support it! If you play the vdr file in something like mplayer, can you see the VBI data at the top of the picture? Or is it transmitted some other way?

[Harry]

oops...*gg* i completely misunderstood you..hehe.

to be honest.. i have no idea how the teletext is extracted from the dvb stream and
put into the VBI.
i have to investigate that.

cheers
Harry

[torsten]

Hi,

as far as I can remember it is in a (private) stream of the .vdr. One should have a closer look at the osdteletext plugin to get more details. If you use a card supported by the ivtv-driver (analog!) the teletext can be saved into the TS/PS stream.

In DVB teletext has its own pid-number. This can be easily seen in channels.conf of the vdr.

Yours

Torsten

[Chris]

I know how the new digital DVB teletext system works, with graphics, nice fonts, more interaction, not necessarily page numbers etc etc works. We are definitely not talking about that here?

[Harry]

that is correct.
we're talking 80's block-like screens with a total of 96 letters, digits and special chars.
(transmitted between line 577 and 625 AFAIK)

there's a new form of text embedded in the DVB stream?
didn't know about that.

[torsten]

The teletext transmitted via DVB-T looks the same as the analog one via cable. It is the 80's block like screen. But there exist different versions of teletext. It was extended over the years. What you'll see depends on the teletext decoder of your tv-set or your vdr respectively.

So I'm of the opinion that we did talk about the same.

Over the weekend I'll try to have a closer look on that.

Yours

Torsten

[torsten]

Hi again,

did you think I was talking about MHP? I wasn't.

Yours

Torsten

[torsten]

Hi,

here is a snapshot from my vdr.

Torsten

[Harry]

thanx 4 the info.

hmm.. my VDR ist positioned in the cellar... i use it solely for streaming to MVPs.
so , even if VDR is able to decode and display teletext... question remains whether
vompserver can interface with that.

[Chris]

Hah, incredible. As far as I know nothing like that is transmitted on UK-DVB-T. We have MHEG streams which is as I described before, nicer looking fonts, backgrounds, proper graphics etc. So, I would imagine the old teletext data has it's own PID in the TS streams, that could easily be sent to the MVP, possibly easily demuxed by the demuxer (but that would require some work) and then not so easily rendered on the MVP. As they don't transmit it here errr.... someone else could write the renderer ?

[Harry]

renderer?
so... back at the beginning... this text data can _not_ be put into VBI line space?

[Chris]

Well I have no idea how it is transmitted at the moment, but I would hazard a guess that if that data is not in the VBI to start with then no, it can't be put back in. It would involve decoding the MPEG for the picture, making the frame bigger, somehow inserting graphical dots into the top and re-encoding it for the MVP. Then, would the tiny dots of VBI data survive MPEG compression? That is beside the point of not taking all that CPU power on the vdr server.

But, how was that screen shot made? That can't have been the TV rendering the text because you can't take a screenshot of that unless you resort to taking a camera to the TV. So however it is done in VDR could be the way to do it for VOMP.

[Chris]

Hmm, also, another conceptual way of doing it would be to transmit the teletext data as a digital stream to the MVP and have the MVP render the dots using the OSD system. But I very very much doubt the MVP would be fast enough to do that.

[davep]

I think the problem here is that there are several different systems in use around the world, and everyone assumes that their system is *the* system.

AIUI (and please correct if wrong!) the text systems currently used are:

MHEG-5, used on DVB-T in the UK and Finland. This is an object-oriented approach, using something like XML but encoding the data stream using ASN.1.

MHP, used for DVB-T elsewhere in Europe. Simpler XML-based system.

Teletext as used on DVB-S in Europe excluding UK. This I presume is the one being discussed.

[torsten]

Hi,

the screenshot was made via the xine-plugin from my vdr.

In fact the teletext analog and via DVB-T are identical. Additionally there is a MHP Stream on the DVB-T Channel.

BTW

The osdteletext plugin uses a kind of teletext server which caches the pages on the vdr. So you are able to read a teletext page of a different channel or access the pages very fast. Unfortunatly there is no TOP videotext implemented.
Couldn't we use this server too?


Yours

Torsten