grainy captures

[joeatact]

from time to time my captures are dark and grainy while the next one is excellant. What may cause this? I use a WinTV PVR-350 tuner card on a fast pentium off a satelite box.

Joe

[Rich A]

Originally posted by joeatact
from time to time my captures are dark and grainy while the next one is excellant. What may cause this? I use a WinTV PVR-350 tuner card on a fast pentium off a satelite box.

Joe

It might be the nature of your Sat. feed. That's one of the problems with digital signals. The Sat. feed is an already compressed transport stream. When you do the encoding with the PVR encoder you are starting with a source that is already compressed. In some cases I've seen where the Sat's (or other digital medium) can change from a relatively high bit rate to something lower.

The best signal source for compressing to mpeg (what our PVRs are doing) is a clean uncompressed analog video. While the digital signals look GREAT while viewing them, you are seeing the first generation ... take that great looking signal and re-compress it further and the quality will drop.

This is one reason my own setup is using an analog cable tv signal. It's very clean and the resultant mpeg produced is near DVD quality. However in a few years the US FCC has decided that all TV will be digital.

This problem is a commonly discussed one on the ReplayTV / TIVO forums. Again, they are PVR devices that are re-compressing the source. If you have a really good digital signal, you would probably be okay for re-compressing. But you can have it lower in quality just enough to NOT be noticable when veiwing direct, but low enough to adversely affect the mpeg encoding.

A "grain" in the pictures can also be caused by a slightly noisy signal.

[joeatact]

Thanks for the reply

[Rich A]

Originally posted by joeatact
Thanks for the reply

I don't know how or even if you should try a low power amp. Something like 7 to 10 db max. Better consult with your provider first. But if you were to up the signal a tad and if it WERE a noisy (weak) signal it might tell you something.

I noticed something similar here even with my analog cable tv. We have two NBC feeds. One is on cable channel 4 and the other on cable channel 13. I actually can see quite a difference between the two. 13 is MUCH cleaner for some reason. So when I need to record something off the NBC network I just make sure it's available off channel 13 and record there.

[joeatact]

I don't think its a signal strength problem because it can go for days with excellant results. I don't think its a driver problem either. I am woundering if its a cable or splitter problem now. Attached is a link to a sample of what the video looks like. This clip does have some white noise in it but most of the time there is no white noise.

http://www.trade80.com/Mpeg/Test.mpg

[Rich A]

Originally posted by joeatact
I don't think its a signal strength problem because it can go for days with excellant results. I don't think its a driver problem either. I am woundering if its a cable or splitter problem now. Attached is a link to a sample of what the video looks like. This clip does have some white noise in it but most of the time there is no white noise.

http://www.trade80.com/Mpeg/Test.mpg

Thanks for the sample. I notice you are doing an SVCD capture. 480x480 with low bit rate (2-3 mbs) Are you talking about the horizontal flicks (lines) going across the screen? It kind of moves up or down. If so, that really looks to me like some sort of interference getting into the signal. You mentioned splitters. That would be the first thing I'd look at. Could even be a loose connection. All the coax connectors should be tight. Also, you don't want to have any unterminated connector. Like a splitter with one leg not having anything attached. They should be capped with 75 ohm terminator resistors. Good grounding as well.

I'd run a temporary dedicated line right from the source to your setup with no splitters etc., just to see how it looks.

The actual video (disregarding that interference) has a "coarse" or grainy look. Almost like a very weak signal. I'm curious why you are using SVCD capture profiles? Although I doubt that is the cause .. try doing a 1/2 D1 DVD capture. 352x480 at around 4 to 5 Mb/s and 48 khz audio. That would give you a ready to author DVD proper mpeg. Might look better than the 480x480 in fact. I've never tried to do 480x480 with my PVR-x50s.

BTW, I've got 6 out of the 7 years of episodes for Stargate SG-1 burned to DVD .. Two episodes per disc .. Full DVD (720x480 @ 8.8 mb/s) Really nice. I'm missing most of the sixth year's episodes. So I'm watching for them to show up.