[mythtv] XV, alternative output & independant OSD resolution (was: Overscan GUI problem)

Bruce Markey bjm at lvcm.com
Thu Jan 30 04:04:02 EST 2003

Erik Arendse wrote:
> At 29-1-03 13:12, Bruce Markey wrote:
> I have no choice in this matter, whatever ergonomic guidelines are. I 
> target a PAL display (close enough to NTSC for this discussion). 
> Teletext (and thus our subtitles) is fixed at a 25 (well, for this 
> purpose I could use 24) lines 40 columns grid. I suspect if you have 
> vision- as well as heading deficiencies you just have to read a book 
> instead of watching TV :-)
> BTW: If you never saw a teletext system resolution, just think Commodore 
> 64 on a TV, it's exactly the same.

Is there a big blob in the middle of the asterisk? ;-)

I've certainly seen a Commodore to understand that amount
of text but I've never seen teletext. 25 lines does seem
aggressive but possible with 576 lines.

> I have never seen a US close caption system myself but I presume 
> character sizes are similar. I could not find any screen shots either, I 
> only read that some TV's support different fontsizes. No idea how that 
> is supposed to work, do they wrap lines on the fly, or does the right 
> and bottom part fall outside the screen (seems useless to me)?

Close caption seems to be more like a simple markup language
rather than a defined layout. It appears to me that different
TV's have different fonts that are generated in the TV set
and overlaid. There seems to be some simple instruction to
put text at the top or bottom, italic, and even codes for
colors. Two TVs side by side might wrap lines in different
places like two different web browsers wrapping paragraphs.

> So you end up with vertical 240/24 =10 by 320/40=8 pixels for a 320x240. 
> And that is including linespacing...

So half height PAL at 288 may be enough room but 240 is getting
down to no more than 6 or 7 lines for lowercase.

> Luckily as a rule (not the norm, but 95% of the channels) subtitles are 
> flagged as double height, but this does not solve the few single-height 
> transmissions or the same problem in the horizontal direction.
>> If you must have total control of the font res you may want to 
>> consider putting
>> another X window stacked on top but that opens up a whole
>> new set of problems (which were avoided by putting the OSD
>> inside the scalable frame).
> Any pointers? I would really prefer having a transparent background 
> behind the characters, although normal TVs display teletext subtitles 
> with a filled character background, usually black. I heard US closed 
> captioning displays color on black as well?

It usually cuts a black rectangle around each character so
the screen has these black stripes that grow left to right
across the screen covering up everything in its path. Very

I claim no expertise in X programming and planned to send you
"xruler" as a source code example of a simple frameless
transparent window. However, I couldn't find the source until
I looked at the executable and saw that it's a shell script(!)
I'll attach it anyway just because it's cool. Xeyes may be a
better example of a frameless transparent window. It's more
an example for the X SHAPE extension which you may not need.

If you do manage to make an overlaid text window, you'll
probably want to Create it in XvVideoOutput::Init (XJ.cpp)
to fit on top of the video window. You should make a resizing
function then call it in XvVideoOutput::ReConfigure which is
called on ConfigureNotify events.

--  bjm

PS Do you have any suggestions for PAL recording sizes?
I assume 576 and 288 for heights. Are there any suggested
widths common for PAL DVDs, DVRs, VCDs, etc.?

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