[mythtv-users] DVI connection overscan

Rich West Rich.West at wesmo.com
Sun Apr 15 08:48:55 UTC 2007

Alex Malinovich wrote:
> I have my Myth box hooked up to my TV via a DVI-to-HDMI converter cable.
> The video card feeds DVI out, and the TV takes HDMI in. What's strange,
> however, is that I still get a fair amount of overscan on the TV. I had
> thought that in the case of DVI and newer connections the full signal
> resolution is sent to the TV as part of the signal so no overscan is
> needed.
> I've overcome this with Myth by manually scaling the window, but I'd
> prefer to not have to do that and to instead have the full screen
> properly displayed. I had heard that the nvidia-settings utility has
> overscan compensation, but I'm pretty sure that that's only when using a
> TV-out signal, not a direct DVI signal. (If that setting is still there
> with a DVI connection I certainly can't find it, and the interface
> really isn't all that complex.)
> So anyone know what's causing the overscanning and how to fix it?

Other responses hit on how to fix it, but the answer to your "what's 
causing the overscanning" question is simply that it was designed that way.

All of the inputs on the TV, aside from a "PC" connection (be it 
designated as PC - VGA or PC - DVI), are pre-configured for some 
overscan.  It varies per TV, with some brands of plasmas and LCD's 
having ~3% overscan, to other TV's having as much as 11% overscan.

The HDMI input is no different in the _type_ of signal than the 
component input (of course, the signal is all digital, and it can be 
coupled with audio, but you get the point).  The "PC" connections on 
TV's are the exception to the rule.

A prime example is this plasma that I just got.  In the manual, it has a 
grid of all of the available resolutions for all of the inputs.  The 
component connections are hard configured to accept 480i, 480p, 720p, 
1080i at a couple of varying Hz (60, 70, 75, etc).  The HDMI connection 
is the same, except that it can display 1080p.  The list for the 
resolutions available for the PC connection is huge, allowing for finer 
tuning of the picture with absolutely no overscan.  Of course, that's 
where things get tricky as the configuration can be a pain, with both 
the graphics card and the limitations/specifications of the TV.

You might want to check the config on your MythTV system.  If you have 
an nVidia card, check out the wiki entry for ComponentOut (it applies to 
"HDMI in to TV", too).  The nVidia drivers (the later ones) have some 
pre-configured "modelines" which send 480p, 720p, and 1080i signals 
without the need for an actual modeline.

For example:
#------------480p Group-----------------------------
#Option "TVStandard" "HD480p"
#Option "metamodes" "CRT: 720x480 +0+0"
#------------720p Group-----------------------------
Option "TVStandard" "HD720p"
Option "metamodes" "CRT: 1280x720 +0+0"
#------------1080i Group-----------------------------
#Option "metamodes" "CRT: 1920x1080 +0+0"
#Option "TVStandard" "HD1080i"

Or, you can specify the resolution you want in the Display section, and 
the driver will do the rest:
Modes "1920x1080_60" "1280x720_60" "720x480_60"
For 1080p, 720p, 480p respectively....

Not sure if any of this helps you, but I thought I would put it out 
there since I've had some pretty good success with it...


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