Restart background music.

No.
The thing is that it's a couple of scenes with same bg music which includes dozens of movies and before&after each video it changes volume of the bg music + the restarting thing. No wonder it's so messy.
Sure i can't make a classic adventure game.

Hmm... Without seeing what you are trying to do / are working with, it's a bit hard for me to provide a solution.

All I can tell you is that it should be possible to play a video have the background music & / or manually started sounds continue playing while a movie is playing without the sounds being manipulated in any way whatsoever.

Sorry for not being more concrete...
But i sorted it out finally, the problem was the changing volume part.

I was reducing the volume before each video to the player could hear the voices clearly and after the video i set the volume back. It looked like this.

1 music volume = 10
2 play video
3 music volume = 90
(& when fail) 4 change to the first scene

And the third step was causing the music playing for a few ms, before restarting the music, guess not clear enough again, but it's working now...

Yeah not sure what you are on about, but glad you sorted it out.

I fell like a ceated pointless thread but yeah.. It's sorted.