[mythtv-users] PVR250 Settings?
petel at cs.cmu.edu
Thu Feb 12 10:16:14 EST 2004
I've been pretty confused by this whole size/bitrate issue for a while.
Like you, I've been a tiny bit annoyed at a slight loss of video quality
compared to direct-from-digital-cable-box or even compared to my TiVo. (I'm
probably being somewhat anal-retentive about this --- no one else in my
family really notices the difference unless I ask them to look really
hard...). I'm also using a pvr-250 for capture, and would say that my
capture quality is very similar to yours.
At the moment I am capturing at 352x480, with a bitrate of 6000. I've tried
higher resolutions, all the way up to 720x480, but frankly see no
difference, and in fact sometimes the image gets worse unless I am also
increasing the bitrate at the same time. (I'm viewing on a 42" hdtv plasma
monitor.) When I keep the resolution constant and then vary bitrate from,
say, 1800 up to 6000, I get a sharper (even somewhat brighter-looking)
image, though not dramatically so. In your samples, for instance, I see a
very slight improvement as you move from your 2.5/4.5Mbps bitrate sample up
to the 8.0/10.0 Mbps bitrate sample, particularly in the lighting detail in
the background trees and leaves. So I see definite improvement with
increased bitrate, but it is really marginal.
Others (notably Jarod) have observed image quality that is on-par with
direct-from-cable. I get that with my TiVo, so I know it is possible. But
I'm just not getting that right now with my Mythbox. For a while I was
blaming my video card (GF4MX440, using vga output direct to plasma monitor),
but dvd's played via xine look stunningly good, so it seems to me that the
video card is blameless, and that the captured video is itself inferior in
quality. I've also tried the experiment of copying some of the mpeg files
to my G5 Mac with cinema display, and again I see inferior quality when
compared with the EyeTV unit on that Mac.
My conclusion, then, is that somehow I may have an inferior pvr-250 card.
I'm planning to add a second card to my mythbox within the next couple of
weeks, and so perhaps I'll see different capture quality with the new card.
Or maybe everyone else is fooling themselves into believing that their
capture quality is better than it really is (though I doubt it... ;-)
On Thu, 12 Feb 2004, papenfuss at juneau.me.vt.edu wrote:
> On Wed, 11 Feb 2004, Jarod C. Wilson wrote:
>> Might as well top-post, since everything else in this thread is
>> I use 720x480, 8000Kbps for all the stuff I plan to watch on my HDTV.
>> You can see the difference with lower bitrates. Most of the stuff I
>> record for my kid, which will be watched on an analog tube, I capture
>> 480x480, 4500Kbps. I don't keep much around long, and stuff I want to
>> keep I transcode to mpeg4.
> Boy, if you are recording at those rates and seeing a difference, I
> just have to wonder if my card is hosed somehow. I cannot see any difference
> in quality above about 400x480, although I can see mpeg artifact reduction at
> higher bitrates. Makes me wish I had another card for a comparison.
> Anyone have any video clips taken with a PVR-250 at differing
> sizes/rates for some objective comparisons? I nabbed a few frames showing the
> softness problem and put them up on:
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