Hello ValentineHuff,
If you cannot find the recorded video in your output folder, it was not saved.
If you minimize the game or if the resolution of the video has changed, Bandicam will stop recording, restart a new recording or the video will not be saved properly.
You may press the pause hotkey (Shfit+F12) before you minimize the game.
Regarding the audio issue, please refer to the following link.
https://www.bandicam.com/faqs/multiple_sound_recording/
Thank you.