How it works for me...

For all custom resolution mods, there is no need for adding the seta cg_fov line.
Just make sure you set:

STEP 1.
seta r_customwidth "XXXX"
seta r_customheight "XXXX"
seta r_mode "X" --> seta r_mode "-1"
seta com_introplayed "0" --> seta com_introplayed "1" (to avoid the intro video)

to your specific resolution - for me its 21:9 (2560x1080px or 3440x1440px) and

STEP 2.
- go to your Gamesfolder (mostly) C:\Program Files (x86)\Steam\steamapps\common\Call of Duty
- right click on the CoDSP.exe - options - compatibility - high DPI - make the point at the bottom for high DPI scaling and make sure it is stays on "app".

Thats it! :)

For anyone still trying to fix aspect ratio after changing resolution. I changed my windows settings scale to 100. It was 125 previous and that fixed it.

If you want to use widescreen in multiplayer (can't change FOV there) without the "zoomed in" effect, you need to create a custom resolution in your NVIDIA/AMD panel that cuts off a bit of width, e.g. 1440x1080 if your monitor is 1920x1080 or 1920x1440 if your monitor is 2560x1440. Then set the same resolution in the config. You should now have widescreen but without the zoomed in effect (the image will be a bit stretched though).

It worked well but how do I fix the stretch?

Thanks for this guide! Its great to see this game in a modern day resolution. 1280x1024 just wasnt cutting it.

Here are a couple of fixes for some errors that I ran into, but figured out:

1st Issue "Config CFG" file isnt showing up in the "main" folder:

You wont get the config cfg file until you have launched the game at least once.

2nd issue OpenGL wont let you start the game after changing the resolution:

The Open GL error only appears if you dont set the height and width parameters in the correct areas.

This is how the guide shows you it will appear in your CFG file -

seta r_customwidth "XXXX" --> seta r_customwidth "1920"
seta r_customheight "XXXX" --> seta r_customheight "1080"

This is how it appeared in my CFG file -

seta r_customheight "1080"
seta r_customwidth "1920"

Notice the height and width adjustments are in reverse order. Make sure the correct values are in the correct spots based on the resolution you are seeking.

Doesn't work for multiplayer tho? It crashes because of OpenGL.

Thank you this was very helpful and easy to do now I can play the game at full resolution

What does seta r_mode "-1" do?

config.cfg for cd version go AppData\Local\VirtualStore\Program Files (x86)\Call of Duty

I can't to find confing cfg, help I have retail cd ver.