Avidemux is a relatively simple to use video editor. It is cross-platform, free open source software (FOSS), so you can use it on Linux, Windows or a MAC box.
Illustrations in this post are from Avidemux running on Lubuntu Linux.
Before we start, there are a few points which need clarification.
Do you have a Raspberry Pi you are not using, or (like me) have a Pi which is only used infrequently, just to try out ideas?
Why not connect it to your stereo and put it to use as a music box.
One of my RPi boards is just used for the occassonal experiment. So I thought I'd load my music files onto an unused 4GB sd card and put this Pi to use.