[mythtv-users] Can't get my projector to work with Myth

[Stephen Worthington]

On Sat, 2 Mar 2019 13:58:56 -0800, you wrote:

>Someone must know the answer to this really fast.
>
>Myth has HDMI output connected to a TV at 1080 according to the TV. I want
>to connect to my projector that is capable of a 1080 input.  I also have a
>small monitor connected to Myth via RGB input but it also has a DVI input.
>The cable to the projector is DVI but the projector is HDMI.
>
>I inserted an audio stripper box so that my cables would work and with that
>box I can play Myth into the TV just fine. I can connect and disconnect and
>everything is happy.

>Myth is setup to not auto detect the monitor as that
>caused all kind of problems. Maybe that is the problem but if I enable
>whatever the hell that function is called, I just get black TV screen
>because when the TV is turned off, Myth disconnects and never reconnects.

The problem of disconnection when the TV is off has a number of
different solutions, most of which have been mentioned on this list at
some time.  Your solution may not be the best one, as you do need to
detect the video device when it changes to something else. Suppressing
the DPMS screen blanking works for some people, and so does killing
one piece of software that I forget the name of.

>Bottom line is that if I insert the projector or monitor DVI cable into the
>audio stripper instead of the TV, I get nothing.

I am not familiar with audio strippers, but I presume that they will
have to decode the HDMI data, and do a digital to analogue conversion
of the audio data to analogue outputs.  I would have thought that they
would pass through the full HDMI data to the HDMI output, still
including the audio data.  But because of HDCP, they will have to
fully decode and re-encode the data, and unless that is done properly,
they may interfere with the normal detection of the video device.  So
I would recommend trying to connect without the stripper in place and
make that work before adding it back in again.  And I am not sure you
actually need the stripper.  Most PCs have a builtin sound card on the
motherboard with audio outputs.  You could be using that to send sound
to your amplifier.  That is what I do - I have the sound card set up
to send S/PDIF audio to my DAC which does the digital to analogue
conversion and sends it to my amplifier.  You can set things up so
that the audio is sent to both the sound card and to the HDMI audio
outputs at the same time.

>I don't understand why the computer doesn't just output its signal and the
>Projector detect it and display it.

The signal needs to be correct for the video device.  A signal that
works with the TV is not necessarily going to work with the projector.
Normally, when a new video device is connected, X will fetch the ID
and EDID data from the device and use that to determine the correct
format for the output data to the device.  It logs what it does, so
there may be information about your problem in your Xorg.?.log files.
Complicating matters is the problem that many video devices actually
send EDID data that is not completely correct, and that can then lead
to the need to override that bad data with xorg.conf settings.  The
fact that it "just works" with your TV simply means that you got lucky
and your TV works well.  Your projector may not be as good.

One thing to try is to shut down the MythTV box and plug in the
projector and boot using it only (no TV or monitor connected, no audio
splitter).  You should get the BIOS screens on the projector, and then
hopefully the PC will boot up properly and detect the projector and
work with it.  Then you can check the Xorg.0.log file and see what
works with the projector.  Repeat with the TV only, and compare the
two Xorg.0.log files and see what is different.

>I look in xorg.conf (is this still the right file? Probably not...) and I
>see my monitor which is identified as a samsung, and the tv, which is not
>identified so why should it care?. It has an output listed as 1920x1080
>which the projector supports.

Yes, xorg.conf is still normally the right place.  But you have not
told us what Linux distro you are using, or what your video card is.
Both matter in sorting out video output problems.  In the worst case,
you may need to have separate manually created sections in xorg.conf
for each of your video devices that specifies how to talk to them.

>The goal is to be able to unplug the TV and plug in the projector and watch
>the Oscars, or any other significant show on the big screen occasionally.
>Normally the Projector is hooked up to a DVD player. I guess I could get a
>new preamp that switched HDMI but that is a huge expense for something we
>would only want to do a few times per year.

And a new pre-amp would not necessarily fix the problem anyway.

>Anyone know what I should do?
>
>Allen