[mythtv-users] Display weirdness

Stephen Worthington stephen_agent at jsw.gen.nz
Sun Sep 13 07:59:02 UTC 2020

On Sat, 12 Sep 2020 20:05:05 -0700, you wrote:

>I thought I had a thread about this already.  Maybe it was buried in some
>other thread. If so I apologize that I can't find it.  I am having two
>problems after a recent rebuild/upgrade with ubuntu 18.04/myth31, and I
>don't know if they are related.
>One is that the screen is going black at random times.  So far this has not
>happened while I was actually watching a recording, but after the frontend
>has been idle for some time.  Just now it did happen immediately after
>reboot and before frontend start, so it's not being caused by the frontend.
>When this happens there is no reviving it.  From the frontend machine
>ctl-alt-f2 does nothing.  I tried SSHing from another machine and
>restarting Gnome.  No help.  Reboot is the only option. It's not that the
>video output is completely going away altogether bc my monitor tells me
>know if there's no signal.  Its just a black screen. This has been
>happening since I rebuilt the system but frequency has been increasing. I
>assume it's a problem with x-10 or the video drivers.

Have you ensured that all the sources of screen saving are turned off?
It does not actually sound like a screen saver, as that should just go
away on any keyboard input (or IR remote input).  But it is worth
checking.  Gnome has options somewhere for settings for xscreensaver,
but you can also just kill the xscreensaver process to test if it is
the problem.  The other problem I have always had is DMPS, where X
blanks the screen.  There is an option to disable DPMS in xorg.conf:

Section "Monitor"
   Option "DPMS"   "false"

That does not always work - sometimes DPMS still seems to be enabled
somehow.  If that happens to you, try these options that allow DMPS to
be enabled, but individually set all the timers that cause it to blank
the screen to disabled:

Section "ServerFlags"
        Option "BlankTime"      "0"
        Option "StandbyTime"    "0"
        Option "SuspendTime"    "0"
        Option "OffTime"        "0"

To get those options to work, you may need to set the DPMS option to

>Today a new problem cropped up.  From the program guide I started ESPN HD
>from the "watch this channel" menu item to watch Lakers v Rockets.  HDPVR2
>started fine but the picture was shrunk to about half the size of the
>monitor. Esc and try again, same result.  Rebooted, and same result.  I
>noticed when it was starting from the program guide it showed the ESPN HD
>icon, but another tv icon with SD below it.  So  somebody thinks they're
>getting a SD signal. You can get HD video off component video outputs of
>the HDPVR2, right?  Here's the kicker.  After watching the game on another
>system, I went back and tried ESPN again on the Myth box as above. Now I
>still get the TV/SD idon on startup but the picture is full screen. WTF?!?

There can be a number of things that can cause this, including bugs.
But the things to look at are how you have the config set up for
playing video.  There are options that allow the video playback to
change the video mode separately from the GUI screens - see Setup >
Appearance > Separate modes for GUI and playback.  If that is set,
then whenever you are playing video, the content of the video is
matched against your playback profiles and the settings for the
matching profile are applied.  This can also cause xrandr commands to
be sent to the X display to get the display to change mode to a mode
that matches the video that is being played.  Such mode changes can
happen if the video being played changes mode in the middle (eg sport
is 720p, but it changes to 1080i for the ad breaks).  The available
mode changes are the modes that X lists in its Xorg.0.log file when it
starts up.  You can get a problem that there are modes available that
are not actually what you want for your screen.  So if the recording
is 576p, for example, the matching mode may be only for displaying on
1/4 of the screen, when it should be set up to reprocess the frames to
a 1080 screen size.  I have just been fighting a slightly different
version of this problem where I do not want any interlaced modes used
as when there is onscreen GUI overlaying video output, the GUI part of
the display gets distorted by the interlacing.  The solution I am
currently trying for this is to tell X not to use the EDID sourced
modelines (and lots of other modeline sources) and just to use the
modelines I have specified in my xorg.conf file.  I turned on this

Section "Screen"
  Option    "ModeDebug" "true"

so that X logs details of all the modes it sees and edited the output
of that to create the modelines I wanted, then disabled all the other
modes.  Along the way, I had some modes from other sources still
enabled that caused exactly what you are seeing where the video only
used part of the screen.  After turning off those modes, it now seems
to be working well, but it has only been a few days so far and I need
to test it on various video files to be sure.

You can find out what mode your screen currently is in by opening a
terminal and using xrandr.  I hate xrandr - it is difficult to use and
does not actually allow you to see the modes in the way they are
reported in X's logs, but the required information is there.  So when
you next have this problem, make sure you have the ModeDebug option on
first, then run "xrandr" and see which mode has the * character by it,
telling you that is the current mode.  Then match that to the modes
reported in the X logs, and see if there is a problem.  You may need
to disable that mode so a better one gets chosen, or you may need to
use an xorg.conf option to set scaling for that mode so it will fill
the full screen.  Your TV may also have a menu or remote key that will
get it to display information about its current screen mode.

BTW You have not said what video card you are using.  I am using an
Nvidia GT1030, so things may work differently if you are using Intel
or AMD.

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