You need to configure aspect ratio scaling in your graphics options. If you can provide the make/model of your video card, we can probably provide specific instructions, but in general, you just need to find the settings for aspect ratio scaling in your graphics card control panel and set it to "fixed" or "maintain aspect ratio". This will make the image stay unstretched, but leave black bars on either side of the image space (pillar boxing).

If you still have an older monitor, anything that fits 4:3, plug it to your PC as a 2nd monitor and go to the AMD/NVIDIA Graphics Control Panel.

Create a new application profile and set the option to force it to the 2nd monitor, I think this option is still there.

Otherwise, use DisplayFusion (or similar) to force specific applications to a monitor; or in Windows Screen Resolution, change the primary monitor.


EDIT: Forgot to mention that even with this setup, you will need to go to the Battle Realms game folder, open Battle_Realms.ini and edit the following lines to the resolution you want:

Width =1024
Height =768

I'm using a 24"W 16:9 LED monitor by BenQ, model GL2460HM. it's native res is 1920 x 1080.

Then i'm also using HDMI cable for it which mean it 'automatically' set stuffs for the monitor setting and less customization can be made in it's menu as if using VGA/DVI cable like in my older computer (not with me anymore, so no extra monitor etc.)

My graphics card is AMD R9 270X. So yeah, i'm using AMD Catalyst CC. I did check it's option but couldn't found any 'forcing' res ratio etc other than that Image Scaling Preferences... Which does nothing that i can clearly see.

What i can tell is that when i start most game, normally, the monitor will show some note that saying,

"suggested monitor resolution: 1920 x 1080".

Which i guess whatever manual aspect ratio setting i made might be 'discarded' by the monitor to optimized it to 1920 x 1080 (16:9)?

http://support.amd.com/PublishingImages/Support/GPU-68/gpuscaling3.jpg

if that doesn't do it, maybe you could just select a 4:3 resolution for your display in CCC, before you start BR. it's not ideal, i know, but i would certainly give everything a try. even just to know if it's at least possible to play BR non-stretched.

in the nvidia panel, i can also select if the scaling is performed on my GPU or my Display.
if you have such options in CCC then i'd suggest playing around with them.
because i found that some games do not scale correctly on one or the other setting. for example warcraft 3 will just stretch if i select Display-scaling, but if i select GPU scaling then it actually correctly keeps the 4:3 aspect ratio and gives me the black bars.

the nvidia panel also has a check-box for "override the scaling mode set by games and programs", if you have such an option in CCC, then give that a try as well. because with this option as well, i've found that some games will still stretch if that box is not checked.

i guess you might as well try disabling/enabling ITC processing while you're at it. i'm not exactly sure what it does on a technical level, but i know it has to do with HDMI interfacing.

btw, on the picture you can see that there's a "scaling options" tab, be sure to have checked it out :-)