Underscanning Rpi4 video out

Support
1

I am building a ‘Retro’ media centre into an Iconic Bakelite 1952 Bush TV cabinet which originally had a 9" round CRT fitted where the top an bottom were blanked off to give the impression it had a somewhat square ish screen. The aspect ratio falls somewhere between the old 4:3 and the more modern 16:9

I am using a 12" 4:3 lcd monitor as the main display and I need to create a custom aspect ratio where I can specify the height and width that I want. The underscan option in the RPi OS just underscan’s very slightly. If you look at the vintage test card on the screen, you will see some thin strips of tape creating a smaller rectangle on the screen, I need to underscan the picture to fit inside this rectangle, so everything the display displays must be inside these tape lines.

I’ve been told this can easily be done in one of the boot files but I’ve not been able to find any information for a noob like me. I am running the 64 bit RPi OS and I am using the HDMI 1 output fed into an HDMI to VGA official adaptor

Can anyone help me with precise information to do this?

TIA

A1
A11200×1600 320 KB

A2
A21920×1440 178 KB

2

I think you’ll get a quicker reply if you post this type of issue on the Official Pi Forum.
Raspberry Pi Forums - Index page
I think they will have a bigger user base that would have tried to do this, or have actually done it.

3

I did actually get a very comprehensive ‘How to’ on FaceBook earlier, that guy knew his stuff. I tried a few suggestions of his which didn’t have the required result and then he went on to explain how to create a custom HDMI boot, I’m playing with that at the moment.

4

Ok, I hope you get the results your looking for. This isn’t something I have ever even remotely contemplated doing. Half or more of my Pi setups run headless with no monitor attached. What’s left is a mishmash of tiny SPI LCD’s, a couple 7 inch touch screens, and a full size monitor or two.