I am running knoppmyth R4V5 and I have a PVR-250 (Model 980, orange box, tuner type 39, R382 IIRC), and an ahtlon 1800, with 512 megs of ram, and an ATA100 7200 rpm Western Digital 60 gig drive

I've searched the forums pretty heavily, but have been unable to find anything addressing a problem exactly like mine. I actually have two problems; my biggest concern is the extremely poor signal quality I'm getting. Although I'm using a good cable TV feed, it looks like i'm watching with a crappy antenna. The biggest signal screwup is light and dark verticalish (they lean to the right a little, sometimes much more) bars. I suspected the coax cable i'm using was the culprit, but on a friend's tuner card it produces a much better (but not perfect) picture. Is this an RF quality issue, or is it a hardware problem? Another thing that may be of note... in order to get the tuner to work right (that is be able to change channels, before it would only show me one channel no matter what), I had to use "cable-us-hrc" instead of "cable-us" in mythtv-setup

My second problem is occasionally I will get short hiccups or pauses every few seconds when watching live tv. They're not very obvious in the video, but obvious and irritating in audio. I have DMA enabled on the drive, motherboard, OS, etc. I'm using a 5200/6000 bitrate at 720x480. If I pause for a while and then play again, it seems to alleviate the problem at least for a little while. It almost seems like its playing the video buffer faster than the tuner card can encode it.



Thanks guys, you have already helped me out; extensive searching of the forums has gotten me as far as I have come.

1. Attach the cable to a regular TV and see if the quality is the same. If it is, call you cable company (I did this several months ago).

2. Run the frontend from and xterm. After it stuffers a few times, quit to see what is outputted. If it is "prebuffering pause"
2a. Ensure Xv is working (xvinfo).
2b. Change the nice level of KnoppMyth-run (-15).
2c. chmod +x /usr/bin/mythfrontend

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cesman

When the source is open, the possibilities are endless!

It is indeed a prebuffering pause, and the output of xvinfo seems kosher; what exactly should I be getting? Also, its been a while since I've done any linux hacking... how do I change the nice level?

Also, I don't have access to another tv in this room right now, but I'm pretty sure the cable feed is good (Certainly way better than what I'm getting, I would think). How plausible is it that it is a problem with the tuner/drivers/etc rather than the cable/connection? Watching it some more, it appears to be almost perfectly straight lines, leaning to the right at about 30 degrees and pretty consistent (Not as variable as I thought).

And out of curiousity, what does chmod +x /usr/bin/mythfrontend do? I mean, I know how it changes permissions, but how does that affect performance?

Thanks

opps, I meant chmod +s. nice -15 KnoppMyth-run. I won't paste my xvinfo, as long as you get info and not "no adapters present" xv should be working.

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cesman

When the source is open, the possibilities are endless!

I solved a nasty persistent signal quality problem by eliminating extra connections, extra equipment, and switching back to using only the heavy duty screw on coax that the cable install guys set me up with. (BTW - I got very lucky when they did my install, I had the local trainer teaching two or three new guys, and he seemed really serious about showing them how to do it right.)

There are several possible components to this.

- Computers can be a beastly source of RF interference

- Most retail "coax" cables aren't all that well shielded.

- Even the best push on connectors apparently have much higher contact resistance and signal loss than the good screw on ones.

- Extra equipment in the circuit can produce interfence even when it's turned off, possibly just by being poorly shielded and thus an entry point for RF.

Having pared my circuit down to just two straight runs from the splitter (one directly to the TV, the other to the PVR-250, and then S-Video to one of the TV's line-in connections, has dramatically improved recording and picture quality from the KnoppMyth box. I'm not kidding about the difference being dramatic either. I spent about half an hour playing with it thinking "Oh, wow..." ever couple minutes, and feeling like an idiot for screwing it up in the first place.

Well its too late to go buy a nice coax cable to try, but more and more, I'm thinking the cable (which is pretty crummy) is the problem. And cesman, as far as your suggestions go, they seemed to help only a tiny bit if at all. Is there a way I can increase the size of the prebuffer?

Not that I'm aware of... Try a search of the MythTV archive for more suggestions.

Well, I just got a brand new heavy duty RG6 cable... looks exactly the same. Could the fact that I'm using cable-us-hrc frequency set rather than cable-us (which doesn't seem to work at all) be the problem?

Well, that was it, I switched to the cable-us frequency set (somehow it works now) and I get a good signal now. I still have the occasional stutter (though it doesn't seem as bad now). The picture quality still seems to be a bit low though, like its at a low res/bitrate, even when I set it to max res and a high bitrate in the record settings.

I am having the same problem. The thing is, last week I had this same tuner installed in a Windows machine, connected to the same cable, and the reception was just fine. Now it's unwatchable, like a really bad antenna. With some channels you can't even make out anything through the static and distortion -- so I am not just talking about "poor" quality.

What I found strange was, most Windows TV tuner apps do an initial channel frequency scan to detect the channels, but MythTV didn't seem to do anything of the sort. Could this be why the reception is so bad? Is there a way I can force MythTV to rescan the channel frequencies?

MythtTV never scans the channel frequencies. It uses whatever xmltv/datadirect tells it to.

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Have a question search the forum and have a look at the KnoppMythWiki.

Xsecrets

Turned out it was my cable/outlet. Weird, because that cable/outlet worked fine with the TV before.

Anyhow, quality is still not very good, but now the quality problems seem to be more related to digital artifacting etc., so probalby software/encoder/decoder issues. I'll search the forums elsewhere for that.