Well I want anyone just starting out in shotcut to know how to add backround music
and its actually really simple. What you need to do is insert your music make an audio track drag music to audio track and then you need to add an effect to the music (Gain/Volume) then put gain/volume at -20 or -10 or basicly any negitive number to avoid the song being louder then the video. Hope this helped anyone
Personally I find it easy to do all audio editing in Audacity and then put that *.wav file in playlist and then add it to Timeline audio track. Audacity is dedicated audio editing software that has a lot of features.
This tutorial is manly just how to have Quit music in a backround of a video.
Videos #2 and #3 in this link show how to add audio, and how to add the Gain/Volume filter.
https://shotcut.org/tutorials/minitutorials/