[mythtv-users] Subtitle (Teletext) recording and PVR-350?

[Joseph A. Caputo]

On Thursday 14 October 2004 10:37, Piers Kittel wrote:
> Steven, Joseph and Rudy;
>
> Thanks very much for your comments.
>
>  > You mention that you read that it doesn't work with a PVR-x50 and
>  > then you ask if it works with a PVR-350... now that's confusing.
>
> Steven - Yeah I realise that, but that person says subtitle support
> isn't available with digital cards and then goes on to mention
> PVR-x50 cards that isn't supported which I know are analogue cards. 
> As you and the others have cleared up, it's due to different drivers.
>  Just wanted to clarify.

Ah, here's the problem -- you're encountering different people's 
definitions of 'digital' and 'analog' w.r.t. tuner cards.

You are probably more correct in your thinking -- a 'digital' tuner is 
one that can receive a digital broadcast, while an 'analog' tuner is 
one that receives a regular analog cable or OTA signal.

However, the person that said subtitle support isn't available with 
'digital' cards wasn't referring to the tuner -- he was referring to 
the output of the card.  'Digital' was probably the wrong description 
to use -- a better phrase would have been 'hardware encoder cards', or 
better yet 'cards that output an MPEG-encoded stream' (as that also 
includes DVB-type cards.

PVR-x50 cards are 'hardware encoder' cards, meaning that they encode the 
received analog signal into an MPEG stream.  However, since the source 
is still an analog signal, these cards are also capable of interpreting 
the VBI data and thus producing a CC or Teletext stream as well (on a 
separate device, usually /dev/vbiX).  There is some support for this 
recent versions of the ivtv driver, but I don't really know how stable 
it is, and in any case Myth does not support CC or Teletext for these 
cards yet.  Once the driver support has been deemed stable enough, I 
imaging support will go into Myth.

Support for digital (DVB or other satellite) tuners is a different 
matter. Since the received transmission is already in MPEG format, the 
subtitles would need to be already multiplexed in the MPEG container.  
Myth currently does not have support for this at all.

> Anyway, this now makes me really nervous of buying a PVR-350 card
> considering as I rely totally on subtitles as I'm deaf - probably
> best thing for now is to buy a cheap analogue TV card for now, and
> upgrade to PVR-350 or direct to the DVB card once subtitle support is
> sorted for either of those?  But then again I've already an digital
> STB and I can use the PVR-350 to record from that as the subtitles is
> "pasted" on the screen - but subtitles on the STB is fairly spotty
> (loses out around 20% subtitles normally at around critical moments! 
> Not sure if it's the STB or my aerial that's to blame).  Hmm
> decisions, decisions...

If you're recording from a digital STB, Myth may not have access to the 
VBI subtitle data no matter what kind of card you get.  Presumably it's 
the STB that's rendering the subtitles onto the picture, after having 
decoded them from the digital transmission (you can probably check this 
-- is the control that you use to turn Teletext on/off on your STB 
remote or your TV remote?).  All Myth can do at that point is record 
the complete picture with the subtitles pre-rendered.

At this point, it would seem that your choice of card is irrelevant as 
far as Teletext is concerned.  You'll have to choose a card based on 
other factors (price, hardware vs. software encoding, etc).

Good luck!

-JAC