I generally put together a trailer and release it about the time the book is published, or at least a few weeks later.
As I mentioned, I do the trailer. It takes some preparation but not a lot. And if you have everything in place, it shouldn't take more than an hour or so to complete it.
One thing I've learned -- at least from my viewpoint -- is to make the trailer as short as possible. My first trailer, for "Foolish Is The Heart," ran more than two minutes. I've questioned whether people really want to watch a trailer for that long.
My last trailer, for "Laments," ran 70 seconds. It's really a minimalist-size trailer since I don't have many images. Why? I suppose because the trailer is so overdue. I can always go back and add images -- if I find the time.
I would guess that any computer with Windows will have software to compose a video. It's not that difficult. And I can do it, well, I'm sure you can do it as well. I'm sure you can find a service on the Web that can produce one as well.
As mentioned, it's nice to have images. I also include music, which is easy to find. Just make sure you have permission to use it. I also give credit for the composition at the end of my videos.
I've included book trailers for my books as well as one I did for Steve Flairty so you'll have see how I've approached each book.
Good luck with yours!