[mythtv-users] Questionable capture quality from a PVR-250

[papenfuss at juneau.me.vt.edu]

> I think a bigger issue may be that you're capturing an interlaced signal, 
> deinterlacing it (presumably) with MythTV, then spitting it out your video 
> card, which then re-interlaces the picture for the TV. This is the primary 
> reason the PVR-350's output is superior -- you never have to deint/reint.
> 
	Interesting that you brought this up.  The TVout I'm using is through
the home-brew NTSC converter, with the VGA spitting out NTSC signal (720x480,
15.7kHz H, 29.97Hz V interlaced).  So technically, I don't have to deint/reint
either.  I did end up turning on the "deinterlacing" in mythtv to prevent some
vertical "tearing."  I had attributed that to the X server setting the dotclock
to 14.32 MHz (instead of my specified 14.318 MHz), and the resulting "beat
frequency" between bone-fide NTSC and my "almost but not quite 59.970 Hz V
freq."  I will check up on that and post back.

	As I think about it further, I doubt it's the deinterlacing on mythtv 
since I saw the same picture issues with mplayer directly.  Also, playing DVDs 
or DIVX's (progressive scan) looks great.


> Also, upon further VERY close examination, I do see the PVR-350's output as 
> being crisper than that of my GF4 (even when using VGA-Component, thus no 
> reinterlacing). The difference I see isn't huge, even when using SVid out on 
> a GF4, but I have a very clean signal going into my capture cards, so that 
> may help. And the issue is NOT capture side (for me), because I can watch the 
> exact same recordings on the GF4 and 350, with different visual results.

	That doesn't surprise me.  The PVR-350 has the potential advantage of 
not needing to do a scanline conversion, and can also genlock between the input 
and output.  Not that it necessarily does, but it might.  The GF[24] seems like 
it should always be at least *slightly* lossy, since it has to do a scanline 
conversion (to match framerate/resolution/timing/etc).  Unless you output real 
NTSC interlaced framerates, but that's another story... :)

> A resounding YES. But I'm not certain exactly how. If you can post up a small 
> clip of what you say looks like crap, I can take a look at it relative to 
> what I'm getting. I still need to get together some sample clips myself, per 
> a request from Cory -- I can share those with you as well.

	I'll try to catch some of my "crap" video too... probably with 'cat 
/dev/video' rather than nuvexport.  Never have played with that yet.
> 
> Have you tried other firmware versions? Some folks have had considerably 
> different results with different firmware versions.

	Haven't tried that either.

> Hmm... From the look of that output, you DO have a rev1 PVR-250, just like 
> Cory. I don't know if that really matters, but I'm suspicious... ;-p
> 
	Me too.

-Cory
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