When entering the output information, you may need to choose a folder, folder+prefix, or folder+filename. Currently if you provide a folder when it needs a folder+prefix or a folder+filename, then it does automatically generate a prefix or filename. If you then change the animation, it doesn't generate a new name because it doesn't know if you want to get rid of the existing name. We could add a button to force it to get rid of the current name and generate a new one, but you'd still need to provide the folder first.