I'm getting ready to build a MythTV box and my big issue right now is how to
get high quality SDTV output from the machine. I do not consider the s-video
output port found on most video cards to be anything close to high quality.
I am not aware of a video card that will output a true 480i signal, all of
the ones I'm aware of force the image through scalers which destroy the
quality. I want to be able to take interlaced video in, keep it interlaced
while it's encoded, and then output it as interlaced video. I am also aware
of the Hauppauge PVR-350, but this card seems to have a number of compromises
with regards to non-MPEG2 output. I do want to use the MythTV box for AVIs,
MP3s and console games (SNES, etc.). I am vaguely aware of Cory Papenfuss's
VGA to NTSC transcoder but my soldering skills are pretty poor and I can't
seem to find the schematics anymore. I've also seen on this list that some
newer nVidia cards can do component output but I haven't seen anything that
confirms that they can do a 480i signal. Also, these cards seem to have some
issues with Xv video acceleration. With that said, I hope some people on
this list know of some cards or tricks that I am not aware of, or areas where
I am just plain wrong. Right now I am only looking for s-video or component
SDTV only.
As far as I know, things are still in various states of
brokenness. The NVidia driver I'm using on an MX-440 currently will
*output* interlaced, but internally throw away one field. The ATI drivers
(open-source) still have the weird bug and I haven't bothered on the gatos
driver since I'm now running xorg.
Bottom line is that what used to be very common (supported
interlaced modes out of VGA cards) is not common anymore. If you wanted
to build something like I did, there are (or at least were) a number of
different schematics/designs out there. Mine is still broken and would
take some effort to clean up. If you don't want to DIY, I'd see if any of
the commercial transcoders can do 480i.
FWIW, I briefly corresponded with a guy at nvidia who says that
the drivers are supposed to disable the scaler when a "dvd-friendly" size
is used (e.g. 720x480). I have yet to hear of anyone who can verify that.
-Cory
--
*************************************************************************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
*************************************************************************
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