[mythtv-users] Match display refresh rate to video framerate

Schuren, Mark schurenmark at versanet.de
Mon Dec 28 09:56:52 UTC 2009

 Jean-Yves Avenard wrote:
> Hi
> 2009/12/28 Schuren, Mark <schurenmark at versanet.de>:
>> - In the relevant mythfrontend settings page I choose 1920x1080 for the gui
>> and video resolutions and "Any" for the refresh rate to enable the automatic
>> mode adjustment. BUT: browsing the available frequencies there does NOT show
>> me "24.0", "50.0" or "60.0" Hz, but gives me the following choices "23.919 Hz",
>> "49.832 Hz", "59.719 Hz", "59.798 Hz" or "Any".
> The refresh rates showing in MythTV is what is calculated from the ModeLine.
> So while nvidia shows it as 24Hz in the nvidia-settings it really is 23.919Hz

I already suspected this to be the cause.

> It looks like the algorithm to select what best refresh rate is usable
> fail in your case because 49.832Hz is too far away from 50Hz.
> the reasons for the code for not picking up 49.832Hz was that I had to
> give a pretty narrow interval checking to be able to differentiate
> 60Hz from 59.97Hz which is what the US really uses...
> So when selecting what the best refresh rate is ; it first tries all
> refresh rates with 0.1 accuracy. If that fails it tries to round to
> the next integer (so that 59.97 shows up as 59 and 60 as 60).
> 49.832Hz as such is picked up as 49Hz which doesn't match 50Hz as far
> as the code is concerned.

> I will have to investigate this further.
> I've never seen refresh rates so far off the real thing.

So either the EDID of my TV reports really strange information, or the

nvidia driver (without using homegrown modelines) does, right? I will play
with your suggested xorg.conf when I get home.

Until now, the result was always the same, regardless which driver version
I used (185, 190 or 195 versions).

> In the mean time ; you could check on my site for a xorg.conf that
> defines the proper refresh rates, so no more of this 49.8Hz garbage.

I will follow all your suggestions as soon as I get home tonight and
come back to it. I think 'xrandr -r' is not a valid command though,
did you mean 'xrandr -q'?

Many thanks for the very clarifying hints so far!


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