I've tried to dual boot with Fedora, NixOS being installed first, but now GRUB menu shows only options for Fedora and I lost my precious NixOS installation. Already tried everything described on Fedora wiki and various Internet sources, but to no avail. Worth mentioning that both os-prober and grub2-mkconfig finds Nix installation but it is not added to grub config.
You can always to squeeze the video using Handbrake.
If you wanna simple video editior softvere, give a try to OpenShot
You can always go with KDEnlive if you're feeling little adventorous. :)