Date   : Tue, 09 Jun 2009 14:14:36 +0100
From   : michael.firth@... (michael.firth@...)
Subject: Morley Teletext Adapter

> -----Original Message-----
> From: 
> bbc-micro-bounces+michael.firth=bt.com@... 
> [mailto:bbc-micro-bounces+michael.firth=bt.com@...
> .uk] On Behalf Of Andrew Benham
> Sent: 09 June 2009 14:02
> To: Joel Rowbottom
> Cc: bbc-micro@...
> Subject: Re: [BBC-Micro] Morley Teletext Adapter
> 
> Joel Rowbottom wrote:
> > Hi Anders --
> > 
> > On Tue, 9 Jun 2009 14:35:29 +0200, "Anders Carlsson"
> > <anders.carlsson@...> wrote:
> > 
> >> While I don't have a clue how digital broadcasts work in 
> the UK, I am
> >> fairly 
> >> positive the DVB aerial broadcasts here in Sweden still 
> carry a teletext 
> >> signal.
> > 
> > I know some satellite (DVB-S) services still carry analogue teletext
> > transmissions, so I have no reason to believe DVB-T would 
> be any different.
> 
> DVB-T, at least in the UK, doesn't have the same sort of 
> teletext.  Analogue
> TV has teletext signals on certain lines in the vertical 
> blanking interval.
> 
> DVB-T has MHEG-5 data contained in carousels which are on 
> declared pids in
> the data stream.  (Sorry for the abbreviation soup).
> The upside is that programmes aren't restricted to a specific 
> set of characters
> and graphics.  The downside is that one needs to do at lot 
> more to decode
> and display it.
> 
The standard exists for the carriage of Teletext over DVB-T (or indeed any
other MPEG) broadcasts -the DVB/ETSI standard is ETS 300 472.

However, in the UK I think broadcasters are discouraged from using this,
as MHEG-5 is the preferred approach.

For other countries, support for this standard is mandated for the STBs,
so I'm sure that UK STBs will support it - its just that most of the broadcasters
don't.

As an aside, several of the analogue channels are carried as MPEG video to
the transmitter sites these days, including part of the Teletext service.

Regards

Michael