Is there a way I can join video and audio but not behind each other. For example: Video goes 2min with no sound. I now merge it with 2min sound and the video is only 2min with sound then.

Bandicut does not support adding audio to the videos.

Currently, Bandicut supports extracting audio from video.
https://www.bandicam.com/bandicut-video ... pport/mp3/

We will forward the feature request to the development team.