[mythtv-users] Plextor Convertx CPU Usage

Brian Wood beww at beww.org
Tue Apr 8 01:46:32 UTC 2008


On Apr 7, 2008, at 2:11 PM, Steve Peters - Priority Electronics wrote:
>>
>
> Beww, how is the performance of your plextor?

I'm pleased, but I'm no longer using them with Myth. I got a couple  
more 150s because I wanted MPEG-2 to support a MMVP.

They worked well with Myth using MPEG-4 mode, that was back at 0.19.  
As long as the drivers have kept up with the kernel they should work  
fine.

I'm using them on a Mac running EyeTV (sorry to mention a non-Myth,  
non-OSS PVR) and they work fine. I've never had A/V sync problems. I  
use that system to record things I never plan to watch but want to  
burn to DVD for some reason.

>
>
> Here is my main issue: I have 2 pvr-500's in my mythbox, but I have  
> these
> annoying vertical lines that show up over every recording, even when  
> the
> source is my cable box svideo input. I don't think it's specifically  
> the
> cards, but something else internally, because when I uplug my system  
> fax,
> the lines lessen, but are still there. So I was thinking of getting
> something USB to try to fix the issue. I'd probably get a couple of  
> these
> convertx's if they are good replacements for my pvr-500's.

I'd try and find out what your hardware problem is. If unplugging  
something reduces your problem that's what you have. Not sure if you  
meant unplugging the fax phone line or your modem card, but either  
means you have problems.

>
>
> What do you think? If I had 2-3 of these guys going, would the pcm  
> audio
> converting (that I heard your system has to do) take much cpu up? Do  
> you
> ever have audio out of sync issues, or any other issues with it for  
> that
> matter?

The main problem I've run into with them has to do with common mode  
interference, AKA AC hum. The problem is that the unit is grounded at  
least 3 ways: The DC power supply, the USB connection and the RF  
connector, and maybe your audio/video inputs. Often these are all at  
slightly different ground potentials, so you have to be very careful  
or you will have visible hum bars in your pictures.

Since you already have the PVRs I'd just keep them if you can fix the  
bar problem. The Plextors buy you extra AC adapters and associated  
cables, as well as the USB cable, but they free up PCI slots and are  
the only way I'm aware of (pending the Hauppauge unit) to do MPEG-4 in  
hardware with Myth.

If I were to buy a USB capture device today, it would be the new  
Hauppauge (in fact I have pre-ordered one), but the cost is a little  
over $50.

The CPU load for audio is basically just real-time PCM decode and MP3  
encoding, not a big task for a modern CPU.

beww



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