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

[Bruce Markey]

Erik Arendse wrote:
> At 28-1-03 00:45, Bruce Markey wrote:
> 
>> Brian Foddy wrote:
>>
>>> ...Also,
>>> I have noticed something wierd however, with the capture size set
>>> at 352x480, the OSD fonts are tiny, almost unreadable.  Other
>>> resolutions work fine.  I haven't tried all the possible settings
>>> to see which work and which don't.  Unfortunately, 352 is
>>> the resolution that works best for my machine right now.
>>
>>
>> Fixed in CVS. The fonts and OSD will scale correctly for any
>> recording resolution in 0.8.
> 
> 
> 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.

> ...The issue is that the OSD is put 
> into the frame to display, which is scaled by XV _after_ that. Which 
> means that although your normal menu resolution can be 800x600, if you 
> are watching a low-res capture (say 320x240) your OSD is displayed on 
> top of the show with that resolution.

That is correct. Displaying at 800x600, the fonts on a
640x480 or 320x240 recording appear to be the same size
but the low res recording has smaller fonts scaled up.

> I ran into a serious limitation here, I have 95% finished implementing 
> subtitling support for Myth, but my machine can't process 640x480 so I 
> am limited developing for 320x240. Which means I nearly can't decipher 
> the subtitles I display :-(

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 was looking at scaling the PIP so that it wouldn't be
mis-shaped if live TV is at an odd resolution. I arrived
at two conclusions; 1) it probably isn't practical to do
any more manipulation of the bits being pushed into the
frame and 2) Isaac is really smart. 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).

--  bjm