[mythtv-users] Simple Question About TV Out Quality

Jim Paris jim at jtan.com
Wed Oct 22 22:05:31 EDT 2003


> I'm using PVR-250 cards (Freestyle) and an nVidia GeForce II GTS for the
> TV-out. The quality is very decent, but not as good as the Tivo on the
> better quality modes. This isn't due to the capture card, it's due to
> the TV-out.

Most of the TV-out schemes through a video card or scan converter have
this problem: they don't match up the scanlines exactly, so you'll
have to deinterlace the signal, and it will get reinterlaced on
display, effectively cutting the vertical resolution in half.

> I've recorded video captured on my MythTV box to DVD and when played
> from a standalone DVD player it's fantastic quality because it's
> properly interlaced.

And at the proper overscan, etc.

> I've heard the PVR-350 cards have TV-out? Perhaps if the drivers are
> more stable and if it's possible to drive the video-out directly from
> the onboard decoder I would expect the quality to be quite high. I don't
> know much about that card or the status of the project though.

The PVR-350 has very good output, yes.  It comes very close to the
quality of my TV's VGA input, with two quality benefits:
  - My TV is progressive scan, and so it will do an automatic and 
    high-quality deinterlacing on the S-Video input, but it doesn't
    expect an interlaced signal over VGA and so I have to do the
    deinterlacing in software there (even though scan lines match up)
  - It gets the frame timing right, so there's no jitter.
but quality-wise there are also drawbacks:
  - OSD must get interlaced by the card, so non-video output doesn't
    look as good and flickers slightly on TV
  - can't do MPEG4, etc, so you're stuck with going to lower video
    quality if you want to conserve disk space

> The only thing I have that beats that is my standalone DVD player
> with the TV in widescreen scan mode. :)

Yeah, you can't beat that. :)

-jim


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