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How to change the resolution of an HDMI signal



  • Hello there,

    I want to split the HDMI output of the Pi in my arcade cabinet to display the cabinet's picture on my video projector for additional viewers at parties etc. But alas, my 720p projector can't display the 1600x1200 picture of my cab ("resolution not supported"). My current solution is a VGA converter, whose signal can be displayed by the projector even if it's 1600x1200. The picture then gets scaled down to an 4:3 area of the 720p accordingly.

    As a perfectionist, and to avoid two cables to the projector for HDMI and VGA, I would like to convert the HDMI signal somehow to a resolution that my projector does support. Alas, any hardware resolution changer I found on the net costs $180 or more, which is overkill for my purpose.

    Changing the original resolution isn't an option either, because I want to have the native resolution on my cab's TFT.

    Does anyone here has another idea?

    Thanks
    Clyde


  • Global Moderator

    Can't you use the tvservice command to change the resolution on the fly when you connect the projector ?

    EDIT: Or, on the same idea, you can use conditional filters in the config.txt to set the resolution at boot time depending on the detected monitor (https://www.raspberrypi.org/documentation/configuration/config-txt/conditional.md).



  • @mitu Thanks for the quick answer, but I'm splitting the signal with an hdmi splitter to both devices at the same time, so that the audience can watch the game that's being played on the cab via the projector. And since the cab's monitor shall have the best picture possible, its native resolution of 1600x1200 is mandatory for the output from the Pi all the time.



  • @Clyde Is it easy to split video on the software level with Linux like it is on a Windows machine with multiple monitors? I'm still learning the basics myself so was curious if something like a USB to VGA or a GPIO to VGA would be possible to configure that way. I see those on Amazon a lot and was always curious myself.



  • @KN4THX Thanks to you, too. Most (all?) Linux graphical desktop environments can output their screen on multiple outputs with different resolutions. With the oldest and (still) most common X.org display server, this can be done in shell scripts by the xrandr tool*. But Retropie comes without X.org or similar display server, and I also remember reading somewhere in this forum that the Pi 3b's hardware can't output different pictures at the same time (e.g. via hdmi and composite).

    * edit: I don't know if tvservice can do anything similar on the Pi.

    In addition to these obstacles and unknowns, I would prefer an external solution to free the Pi from any additional cpu or gpu stress, and (with less priority) to be future-proof from significant changes in the hard- and software.

    That said, if there is a software solution for cloning the output with different resolutions without slowing the Pi down significantly, I would be happy to try it. :)



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