Combining two videos in one

[VictoriaJen]

I was filming vertically, and then switched my camera horizontal. Half of a video needed rotation. I split this video in two halves, rotated the second one which needed rotation and now I could not combine them. I am using "Avidemux" and it suggests me to "resize", "add border" or "crop". But I really do not want to loose some footage filmed in the corners. What should I do?
I am not a pro at those things and am doing such stuff first time in my life in general. I would not mind if the vertical part would be in a white, grey, black background in the final video or something.
Please, help me!

[manono]

I am using "Avidemux" and it suggests me to "resize", "add border" or "crop". But I really do not want to loose some footage filmed in the corners. What should I do?

If you don't want to crop and resize one to match the other, then add borders(add black) to one and then resize to match the resolution of the other. It'll have to be completely reencoded.

If you post the dimensions of both, we can perhaps offer more specific advice.

[VictoriaJen]

Thank you very much! It was exactly what I wanted.