[mythtv-users] NVIDIA

Tom Greer trgreer at gmail.com
Thu Jan 11 04:21:47 UTC 2007


I just realized I have an issue with my frontend and I'm not quite sure how
to address it.

The problem starts because I have a Panasonic 42" EDTV plasma.  EDTV  is not
true HD, since the maximum resolution is 852x480.  However, it accepts  720p
and 1080i input and internally scales it to fit the screen.

My MythTV frontend sports a NVIDIA FX-5200 with a DVI port.  I connect this
to the TV with a DVI->HDMI adapter on the PC and an HDMI cable between the
units.

I have an 852x480 modeline in my xorg.conf file.  I thought this was the
best option, but....

Today, I had the nvidia-settings utility open to verify some settings when I
noticed this on the DFP-0 tab:

Native resolution: 19201080
Best Fit resolution: 19201080
Frontend resolution: 852x480
Backend resolution: 1920x1080

When I hover over these fields, I get this:

"The Backend Resolution is the resolution that the GPU is driving to the
DFP.  If the Backend Resolution is different than the Frontend Resolution,
then the GPU will scale the image from the Frontend Resolution to the
Backend Resolution.  If the Backend Resolution is different than the Native
Resolution, then the DFP will scale the image from the Backend Resolution to
the Native Resolution."

In other words, MythTV (and X) are formatting the output to 852x480 and
NVIDIA is scaling it to 1920x1080, then the plasma TV scales the image back
to 852x480.

The TV is obviously reporting resolution via EDID to NVIDIA as 1920x1080,
which is what starts the problem.

I changed my modeline to a 1080i modeline.  The output looks good - probably
better than the original (maybe that's just my imagination).

But I am doing this on a AMD Sempron 2800+ CPU that can't quite always keep
up.  It would seem to me that feeding the output at 852x480 would be a lot
less strain on the system. (I am assuming that since NVIDIA is scaling the
852x480 output to 1920x1080 that this taxes the system, maybe not.)

Has anyone else run into an issue like this?

Any recommendations on how to proceed?

Thanks for your ideas.

Tom
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