FFmpeg keep different sar and dar in multiple videos

Question

I have two video that I'm working through filter_complex.

First video is 1280x720 [SAR 1:1 DAR 16:9] and the second video is 1280x720 [SAR 203:640 DAR 203:360]

I would like to merge the files with filter_complex keeping original sar and dar both each on final output. Please notice I'm using inputs dynamically, so I need a command that keeps sar and dar regardless of the source files.

I tried using the command

setsar=1,setdar=1

But nothing, second video not preserve original aspect (1280x720 [SAR 203:640 DAR 203:360]) and the output is like first video (1280x720 [SAR 1:1 DAR 16:9]). I would like to keep the original parameters also on second video that seems to become SAR 1:1 DAR 16:9.

Answer 1

Problem was in the source file (second input) that did not respect the correct scales and pads. I solved thanks to this answer https://superuser.com/a/991412. Credits to @LordNeckbeard