[Gllug] Re: xorg.conf for widescren lcd tv

Ryland, Peter peter.ryland at squaregain.co.uk
Wed Jul 5 10:18:49 UTC 2006

On Tue, 2006-07-04 at 23:07 +0100, Minty wrote:
> On 7/4/06, Minty <mintywalker at gmail.com> wrote:
> > From: Ryland, Peter
> > The problem is probably that X can't get EDID info from your TV so it
> > doesn't know what aspect ratio the display is.
> I'd be most interested if anyone could expand on this a little.  Like,
> Which xorg.conf settings could I tweak that might help?  I am well
> aware this might be a stupid ass question.

See: http://en.wikipedia.org/wiki/EDID

Check out /var/log/Xorg.0.log which will contain what EDID info it could
find.  Be aware that according to the standards, you shouldn't hotplug
video signals so some BIOSes expect that you will have everything
plugged in on boot.

Anyway, these types of problems are always down to how the hardware has
implemented its video conversion.  It could well be that it can convert
any standard VESA video mode (like 800x600) into a TV resolution
(720x576 for PAL) automatically.  The TV itself never sees the
resolution that you have in your xorg.conf file, it always just sees a
standard PAL signal.  This is not controlled by tweaks in xorg.conf.

Widescreen I am not so sure about (it's quite complicated to be fair as
there are different ways to send a widescreen signal to a TV while
maintaining backward compatibility with normal TVs), but it could be
that your TV will simply detect a "letterboxed" image and adjust
automatically for that, which is how I have mythtv set up at home.  This
won't use an anamorphic mode of your TV so you will lose some vertical
resolution, but will be most likely to work.  Mythtv seems to pick up on
the aspect ratio of the TV, but to get it to work for movies (even with
mythvideo), I have to specify "-monitoraspect 14:9" to mplayer.

> Given I can get it working correctly on an Apple (see below), is there
> any way I can get the correct settings out of OSX somehow?

It doesn't use X does it?

> > From: salsaman
> > One thing I've not tried on this which might work is a xinerama
> > configuration
> I believe the xinerama stuff is indeed what comes with (K)ubuntu.  I
> can certainly get different resolutions on the TV and laptop (and
> ditto with an LCD monitor - the ones I've tried work a charm - dual
> desktop, draggy droppy between both is sweet.  Laptop is at 1366x768,
> and the monitor/TVs are at 800x600 or some other 4:3 res).

That's not necessarily xinerama.  And note that with separate screens,
normally you can only have acceleration turned on on one of them.  Also,
it's possible to have a different DPI for the horizontal and vertical
aspects, so 800x600 is not necessarily physically 4:3.

> I just can't get the linux box to power the TV at 1366x768 res.
> I got the right cable today that let me plug a Macbook DVI into the TV
> VGA, and that worked a charm.  Not only did the apple get the 1366x768
> resolution correct, without having to click a single thing, it even
> knew it was a Sony TV!
> HTF is it able to tell it's a sony tv via a VGA socket (converted to
> DVI on the laptop end, but still)?

That is likely from the EDID info which is transmitted on the VGA line's
I2C bus.  Check your /var/log/Xorg.0.log and your TV may have even sent
a list of modelines that it likes and all you would then have to do is
provide X with permission to use them by putting them in your xorg.conf.

Even better, can you attach the log to a mail please?

> I'm also going to give a Dapper Drake live DVD a try and see if that
> cannot just figure it out for me :)

It's quite possible that it will work on a newer version as they have
indeed added new default modelines.


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