[FFmpeg-user] Problems concatenating mp4 files: Non-monotonic DTS; previous: 824975, current: 140284; changing to 824976.

[Ferdi Scholten]

I need to concatenate several mp4 files that were taken with a cell phone,
> where some of them are landscape and others portrait. By simply concatenate
> them, the ones that are portrait end up rotated by 90 degrees in the final
> output.
>
> To solve this problem, I decided to rotate the portrait ones one by one
> before concatenating them. However, when I concatenate landscape together
> with rotated portrait, I get the following error messages:
>
>
How did you rotate them?

Did you remove the rotation metadata?

Were the rotated video's reencoded?