[mythtv-users] Capture sharpness

Rod Smith mythtv at rodsbooks.com
Sun Nov 25 22:52:49 UTC 2007

On Sunday 25 November 2007 14:35:16 Jay Mallar wrote:
> Rod Smith wrote:
> > - What inputs are you using? S-video is better, composite is middle, and
> >   coaxial (RF) is worst. If you're using S-video for your TiVo and RF for
> >   MythTV, that could explain it.
> I'm using coax from the STB to the PVR-250 and the same for the PTV-300.

Coax is certainly the poorest input form. If you're using it for both the 
PVR-250 and the TiVo, then this is a constant and so isn't the root cause, 
with one important caveat: It's conceivable that the PVR-250 (or perhaps your 
specific tuner) does a poorer job with coax than with other inputs, above and 
beyond the degradation that coax will necessarily introduce. Thus, I suggest 
you try using composite or S-video instead of coax, at least for a test. (A 
Web search suggests that your SAT-B3 DirecTV receiver has both composite and 
S-video outputs.) If you notice a dramatic improvement on the MythTV box or 
if you want it to be a fair test, you should make the same change on both the 
MythTV box and TiVo.

> > - What type of DirecTV receiver(s) do you have? I've seen claims that
> > they vary in video output quality, so it's conceivable that you've got
> > one with better quality feeding your TiVo and one with worse quality
> > feeding your MythTV box.
> My PVR-250 and my PTV-300 are both connected in the same way, to Sony
> SAT-B3 via coax.  The signal is split off from my dish via a multi-switch.

FWIW, the multiswitch shouldn't make any difference. With digital satellite 
TV, if the signal to one box were being degraded, you'd see no signal or 
blocky digital artifacts, not blurriness.

That said, there's a possibility that one of your receivers is outputting a 
bad signal, even though they're the same model. You could try swapping their 
outputs to see if one is bad, and/or viewing them both directly on a TV. This 
possibility is a bit of a long shot, though.

An entirely new possibility has occurred to me, too: It could be that the 
blurriness is being introduced in the video PLAYBACK rather than in the 
recording. You could check this with known clean recordings -- say, something 
of decent resolution and bitrate downloaded from the Internet. 
(Unfortunately, I don't have any specific pointers to suggest.) FWIW, my own 
system runs at 800x600 resolution output via S-video to an NTSC TV, and this 
works pretty well for me. Are you using the same output method from both the 
TiVo and your MythTV box? What video card are you using in the MythTV box? 
Different cards can yield noticeable differences in output quality, so it's 
conceivable you've got bad output.

Rod Smith

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