Re: Thoughts on VDR evolution - my 2 cent

[Carsten Koch <Carsten.Koch@icem.de>]

Klaus Schmidinger wrote:
...
> When I voted against sending the teletext info as a still frame
> I wasn't really thinking about re-insertion. As far as I understand
> this, re-insertion means generating the same "vertical blank" information
> as in analog videotext. If we send the teletext through this bottleneck,
> I'm afraid we will lose a lot of the possibilities digital teletext
> offers. The VDR PC could chache all of the pages sent and have them
> ready instantaneously. But with re-insertion the information would
> have to be sequentially sent through the video signal's vertical
> blank, and it would be as slow as in the old analog days.

It depends.
If the firmware does the re-insertion automatically, 
you are right: we would gain nothing over analog teletext.
But then it would also be impossible to use this path
for the OSD, so I could not possibly have meant this. ;-)

The path that I envisioned was: vdr reads the teletext 
data from /dev/vbi and collects it on hard disk or in RAM.
However, instead of the OSD it uses re-insertion to feed 
ANY data (which could happen to be collected teletext,
but could also be vdr's own menus) to the TV - on a fixed 
page number (say, 100).

There would be no speed problem at all. Have you ever seen
how blindingly fast teletext pages come in when the station
broadcasts just a few of them? No delay at all.
To be more concrete: I believe that I remember from the analog
teletext specs that one vertical retrace carries about 20
lines of data. That's almost a page. So we would be seeing
a speed of nearly 50 fps! Two orders of magnitude faster 
than the current OSD.

To remove the OSD, vdr would only send a full transparent
page with no text or graphics on it (same concept as in
teletext subtitles - you see no teletext at all between two
blocks of subtitles), so the tv could stay in teletext mode.



> I would have to fiddle around
> with getting in and out of teletext mode.

On my remote control there is a button for this.
Press it once and you are in or out.
No fiddling or other musical instruments required. ;-)

To be more serious: I would be willing to trade pressing 
one extra button when going to another input source for 
a full-speed OSD. Would you not?


> What I would really like to have is a faster OSD.

No argument at all from me here.
That would be the solution, my idea would be merely a workaround.

I, too, would welcome Ralph's comments on speed and
reliability of the OSD. 

Carsten.


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