Thursday, August 11, 2005

NVidia versus 2005FPW in MythTV

I've been consumed the last few weeks with trying to get a working HD PVR working in my Dell desktop. I haven't been posting on this subject, because I think it's pretty well covered elsewhere on the web, and I am too confused much of the time to give coherent advise to anyone. However, I came across a problem which others might be beating themselves up on.

My PVR is composed of a Dell Dimension with a 2 GHz Pentium 4, a pcHDTV-3000 tuner card, an NVidia GeForce FX 5200 video card, and a Chaintech AV710 audio card. I'm using DVI to output to my desktop monitor, a Dell 20" widescreen 2005FPW with a native resolution of 1680x1050. I'm using Fedora Core 3 Linux (Core 4 is out but not well supported by all the other things you want to install, believe me, I've tried). I've installed NVidia's native Linux drivers.

Anyway, the unusual problem is whenever I want to display HD content from my local PBS HD station, which I think is in the 1080i format, it is distorted in a funny way. Every centimeter or so, there is a a wavelike distortion, like someone dragged their fingers through cake frosting. It's horrible.

I did some Yahoo searching. By the way, Yahoo is much more likely to find all the web pages you are interested in than Google. And it turns out someone else was having the exact same problem, and he had tracked it down to the 1680x1050 resolution that MythTV was trying to display content at. Practically any other resolution would be fine, but not 1680x1050. If I go into the MythTV setup, and I tell the GUI to use 1648x1050 with a 16 pixel X inset, it will play without distortion and look beautiful, although there will be these 16 pixel bands on either side of the MythTV where the Linux desktop shows through. I believe the problem must lie with the drivers, something with how they handle de-interlacing and scaling.

I'm still not finished. The audio over SPDIF from the AV710 card stutters horribly, and is not in the proper format for my receiver. It looks like the player is having to slow itself down to try to convert the audio, so everything is in slow motion. I thought the audio was in AC3 format, so it shouldn't convert at all. So I've been up to my ears in .asoundrc files, and getting alsamixer just so, I'm sure I will try this and that, and think of new searches and someday it will just work, and I'll be able to watch some live TV, and it will be very satisfying, but until then it's pure frustration.

Update: I can get full 1680x1050 video display if I use the VGA connector instead of the DVI. I don't know how much quality is lost when using the analog connector, especially with possibly annoying flicker.
 
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