[mythtv-users] Capture sharpness

Jay Mallar jaymallar at gmail.com
Mon Nov 26 19:39:46 UTC 2007

Rod Smith wrote:
> 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.
Okay - it's not my coax connect; I hooked the coax output from my STB to 
my TV and the signal is perfect.  When I run it through my MythTV 
system, I see the sharpness degrade (as well as a bit of color 
saturation, but I think I can correct that with some twiddling).
>>> - 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.
Based on the above, I don't think the problem is my switch either (I was 
mostly issuing disclosure. :) )
> 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.
I'm using an nVidia GeForce 6200 LE, which I would expect to be of 
decent quality.  In fact, AVIs and such that I've downloaded from the 
net and imported via MythVideo seem to display perfectly.  I also see no 
such sharp-less-ness from the MythTV UI itself, only from the captures.  
Also, DVDs play beautifully with no loss of sharpness. 

Update:  I think I found my problem.  I decided to delete and re-add my 
capture card to see what would happen and realized when doing so that it 
was set as a V4L card rather than an MPEG-2 card.  Don't know how that 
happened, but re-adding it with the correct type seems to have corrected 
my fuzziness problem.

I *think* it might have changed when I migrated to v0.21-trunk... but - 
in any case, thanks a million for all the suggestions.

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