[mythtv-users] Video noise or distortion across very top edge of image

Travis Tabbal travis at tabbal.net
Fri Nov 20 16:58:53 UTC 2009

On Fri, Nov 20, 2009 at 9:49 AM, Johnny Walker <johnnyjboss at gmail.com>wrote:

> I've got the HD-PVR running on Component capture of a Motorola DCX3200
> on a dedicated backend.
> I've got a dedicated frontend using VDPAU and 0.22 compiled from source.
> Channel 222 is CNN Headline News (love my Robin Meade). I am seeing
> some sort of video noise or distortion across what seems to be the
> very top pixel of my playback image. This happens in LiveTV and also
> on Recording.
> This morning I used the Shutdown-Menu on the Motorola DCX3200 to tell
> the STB that my TV only handles 1080i and 720p which finally got me a
> full screen image on my Samsung LCD Television. Now that Samsung is
> connected to frontend using the VGA dsub. The max resolution on this
> Tv is 1368x768 so I wasn't going to mess with the HDMI out on my
> frontend's motherboard.
> The motherboard is an ASUS with an onboard nVidia as follows from lspci:
> 02:00.0 VGA compatible controller: nVidia Corporation C77 [GeForce
> 8300] (rev a2)
> VDPAU seems to be working ok out of the box - the distro is MythBuntu 9.10.
> I tried adjusting the Vertical offset in the Setup-->Playback menu. I
> moved it from 0 through 10 (trying each incrementally) and I wasn't
> able to notice any difference. It does seem that each time I invoke
> the LiveTv mode I may get a more or less dramatic experience of this
> noise.
> Does anyone know what this is and how to go about resolving it?
Sounds like the Closed Caption data. You don't normally see it because of
overscan. Try the newest NVidia drivers and see if you can get it to
overscan the TV output just a little to get that row of pixels out of the
visible area of the screen. When using VDPAU, you can't use the scaling and
such built into Myth from what I've read on the list, so you need to use the
drivers to do it. Both of my systems overscan way to much by default, so I
use the "Overscan Compensation" in the Nvidia X setup utility to set it so
that I just just a little overscan, so I don't see that line but I can see
all of the image.

You might have more luck getting overscanning on HDMI as the VGA output
might not support it (it's not generally done on computer monitors). Modern
video cards like the 8300 work pretty much out of the box with HDMI. I
didn't do any setup to get it working on my machine other than making sure
the NVidia driver was installed. Even BIOS/POST show up over HDMI now.  One
of my frontends uses an Asus M3N78 with the onboard 8300 chip. Works great
with HDMI. I'm not using HDMI audio, so I can't speak to that. That TV is
just using the TV speakers, so I used analog stereo out for it.
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