[mythtv] Box Processor Limits

Bruce Markey bjm at lvcm.com
Tue Jan 21 16:38:29 EST 2003

Brian Foddy wrote:
> If its bad enough, you will see skips or jerky motion.  Also, there
> are messages left on the shell that started mythtv (stdout or stderr)
> that to me indicate some dropped frames.
> You note raises a new question for me however...
> Is there a limited collection of resolutions the capture will work
> with?   For instance, I've had good luck with
> 320x240, 480x480, and 640x480.  However I tried 480x360 (1.5 times 
> 320x240) and it dies (some core capable error).

There isn't a specific set but some random thing don't
work. As Robert pointed out, it really make sense to
only use a height of the number of raster lines (480)
or the lines in a interlace half frame (240). Anything
else is doubling a line or skipping every third line or
whatever. Width is a matter of the chip's clock being
set to latch a some point in time and sampling the analog
signal at that point. Any value could work but some don't
so I use values that I've seen elsewhere; 720 is the bttv
max, 640 is 4:3, 480 is the MythTV default, 352 is ReplayTV
"Standard" quality, 320 is a half sized frame.

720x480 640x480 480x480 352x480 320x480
720x240 640x240 480x240 352x240 320x240

Okay, 720x240 makes no sense. You're better off with more
raster lines so I'd also prefer 320x480 over 640x240 for
that virtual size. So, a better list from high to low
would be:

720x480 640x480 480x480 352x480 320x480 480x240 352x240 320x240

>  So I was about resigned  to the standards
> then I saw your note of yet a new combination that apparently works.
> I was trying to stay with the same 4x3 ratio, but apparently that's
> not needed either.

Right, 4x3 isn't needed but if it is played back at the
default dimensions it will look odd. This happens in myth
if you press "f" to leave fullscreen mode. In 0.8 there
is an option to always stretch the picture to 4:3 if
you record at odd resolutions.

--  bjm

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