Hi, while Mixcraft can do basic editing, it may be necessary to use other video tools to get consistent results. I use Mixcraft, Avs Video Editor, VSDC (which is cheap but complicated & there is a free version but it doesn't work properly with sound - I got it to layer multiple videos before I discovered mixcraft has video lanes), Movavi (which I bought just to reliably reverse video - it also changes playback speed , as mixcraft does, but more precisely) & Vegas Movie Studio Platinum 16 (but it wasn't worth the money it cost for me).
If you are stuck with AVI files, you will need to do a transcoding job (Mixcraft stops when trying this). I use AVS video convertor for this. (Note, if buying AVS software, be sure to get the unlimited license otherwise they expect you to buy a copy for each machine or installation, which isn't worth it. otherwise their stuff is great, though they have a small, dated GUI). There are probably free alternatives if you can be bothered searching endlessly for them. Maybe someone else here knows and will advise in the next 24 hours or so.
Mixcraft 8 Pro Studio Build 418 (64bit)
AMD Ryzen 8 Core 3.0 GHz,
2TB SSD etc, 40GB RAM,
Windows 10 Professional
Focusrite Scarlett 18i8 (1st Gen, USB2).