Originally posted by Fries I think iMovie (it's free) on a Mac should also do the trick. You should be able to split the audio from the video and it should be possible to import other audio separately if you wish too. Audacity is a very capable program if you want to improve the sound quality.
Had a look at
iMovie (on MacOS Mojave).
Yes it supports splitting the audio from a video and also supports some basic movie color (including WB) and audio editing. You can delete the split audio track and put another one at the position. I guess that precise positioning is not really possible. But all in all seams to be better than it once was. Export is limited to the given formats.
To create slide shows that also can contain movie parts, I use
FotoMagico Pro. A really nice software. Export up to 4K and no restrictions concerning output format. Downside: no capabilities to edit audio or video using filters, compressors, gate, limiter etc. - only volume, fade in, fade out, ducking for use with another audio track etc. and you can correct color using a color sphere point and contrast.
I guess the best software would be
Final Cut Pro. It should deliver the best tools for audio and video editing in one place. ;-)