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

[Erik Arendse]

At 29-1-03 13:12, Bruce Markey wrote:
>>That is probably not what he meant...
>I know exactly what he meant. In 0.7 the font size was simply
>cut in half if the width was below 400. I've since fixed this
>so that the fonts scale to be within a point of the same
>relative size regardless of the recording dimensions. What you
>describe below is well beyond the scope of Brian's question.
Pity :-(

>First, it is a good thing that you are testing at this res
>since apparently this is common for people using MJPEG.
>I would be more empathetic if the fonts were hard to read
>at 160x120 but at 320x240? I know what you are asking but
>subtitles should be in a font that could easily be read at
>that resolution. They should probably be at least 5% of the
>height. For 240 that would be 12 lines which is more than
>enough for a readable font.
>
>I reiterate that I understand that you are thinking that
>since you have more scan lines, you should be able to use
>higher resolution fonts than the res of the picture. But
>I'm not sure that is a worthwhile goal. The picture has
>to be at a viewable resolution and the fonts have to be
>large enough to be readable from a normal distance.
>"Principles of Digital Audio and Video" by Arch C. Luther
>describes characteristics of vision and viewing ratios
>for different resolutions. NTSC should be viewed from at
>least 7.2 times the height. Fonts should be large enough
>to be read from this distance whether or not they look
>crisp from close range.

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.
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)?

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

Erik