V31 frontend RPi4 UHD vs. HD TV?

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jfabernathy
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V31 frontend RPi4 UHD vs. HD TV?

Post by jfabernathy » Tue Jun 23, 2020 1:27 pm

I've been working to setup my RPi4 4GB as a combo v31 FE/BE using the scripts from Mike B https://github.com/MikeB2013/pi-utils

The testing was done on a Samsung UHD 4K TV even though the run_mythfrontend.sh seems to force it to 1920x1080@60.

But after the testing and setup was complete I moved the RPi4 to my RV camper where it will stay as my mythtv while on the road. It only has a HD 1080P Sony TV.

So my issue is that on the 1080P Sony I do not see as many video artifact with zooming and panning as I do when it's connected to a UHD 4K TV. Is the RPi4 still using 4K framebuffers and logic to process the 1920x1080 mythfrontend picture causing it to look worse on the UHD??

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Re: V31 frontend RPi4 UHD vs. HD TV?

Post by MikeB2013 » Tue Jun 23, 2020 3:24 pm

Jim,

Yes there are differences on in HD and 4K behavior.
For background on why the pi_mythfrontend.json file is required (created by run_mythfrontend.sh) see https://lists.gt.net/mythtv/dev/629820#629820

It should only force 1920x1080@60Hz if /boot/config.txt contains the appropriate hdmi_group=1 and hdmi_mode=16 values.
If you want 4K mode (3840x2160 @ 60Hz) hdmi_group=1, hdmi_mode=97 AND hdmi_enable_4kp60=1 must be set in /boot/config.txt (reboot required if changing any of these values). Without hdmi_enable_4kp60=1 the refresh rate will be limited to 30Hz in 4K mode which will give poor playback.

I only use 1920x1080@50Hz even on my 4K TV (which is LG) as 1920x1080 is highest broadcast rate in UK

Mike

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Re: V31 frontend RPi4 UHD vs. HD TV?

Post by jfabernathy » Tue Jun 23, 2020 5:34 pm

I do have the Resolution set via raspi-config to 1920x1080@60 and the run_mythfrontend.sh shows that at start of mythfrontend. But I think the RPi4 still sees a 4K @30 because of my AV receiver and while the display looks like 1080P, it's having to work harder behind the scenes. The jitter and motion artifacts are much less when connected to a real 1080P TV. My Samsung has no way of forcing it to 1080p. It's 4K if the EDID supports it.

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Re: V31 frontend RPi4 UHD vs. HD TV?

Post by MikeB2013 » Tue Jun 23, 2020 6:00 pm

With Pi4 connected to your AV receiver and mythfrontend playing Live TV you can ssh into the Pi4 from another linux machine and see what the following 2 commands report:

Code: Select all

tvservice -s
tvservice -m cea
The first command should report current screen setting, the second will report all possible screen settings.

Mike

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Re: V31 frontend RPi4 UHD vs. HD TV?

Post by jfabernathy » Wed Jun 24, 2020 9:38 am

MikeB2013 wrote:
Tue Jun 23, 2020 6:00 pm
With Pi4 connected to your AV receiver and mythfrontend playing Live TV you can ssh into the Pi4 from another linux machine and see what the following 2 commands report:

Code: Select all

tvservice -s
tvservice -m cea
The first command should report current screen setting, the second will report all possible screen settings.

Mike
This is good info to try the next time I'm testing an RPi4 on a UHD TV. My combo FE/BE RPi4 is now deployed in the RV and we'll test for real on a trip coming up soon. I'm still not convinced that on a 1080p HD TV that v31 is as good as v30. However on a UHD 4K TV v31 is better than v30 on normal scenes but on pans left and zoom outs, v31 has some very weird artifacts than I don't see on HD TVs or FireTV 4k or Shield TV.

If I were starting over on a budget for home, I'd use RPi4 4GB with HDHR Quatro for my backend and use FireTV 4K sticks for my frontends.

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