Why is my 1920x1920 video playing back in different ratios and scales on different media players?

[XilburQost]

I rendered a computer graphics animation using a square 1920x1920 pixel format, but for reasons I do not understand when exported as an MP4 from Premier Pro it plays back at different formats depending upon the media player:
- VLC media player displays the video as a square, but it is zoomed in and compressed vertically;

- Windows 11 media player displays the video at what appears to be 16:9 ratio with the bottom of the video cut off. 

Why is it doing this? Any suggestions? Thanks. Premiere Pro 23.3, Windows 11

[Ann Bens]

Check the settings of the player as in aspect ratio.

Might want to set them to full screen.

What does the file look like when importing back into Premiere?

[XilburQost · Accepted solution]

Thank you for the suggestion. Makes no difference whether the video player is at full screen or not. I've worked in various formats before without issue; I'm trying to figure out why this one is different.
If I import the exported video back into Premiere Pro it looks fine.

Other observations:
- The Windows thumbnail displays the video as the wrong format just like Windows media player;

- If I check the properties of the video in Windows 11, it correctly reports the video as being 1920x1920 pixels.
WORKAROUND: Exporting the video as HEVC (H.265) instead of H.264 resolves the issue. 

[Michael22097950dv1a]

I had the exact same issue. You're HEVC solution worked, but I really want to know what is causing that behavior. I've never seen it before.  I had even dropped my 1920X1920 files into a 1920X1080 sequence and resized to fit the vertical, but it still exported in that same weird way!