Movie in the background

I was wondering if it is possible to have a video all ready made, load it into blender and then create 3D animations that are put into the movie, like CGI stuff in movies, how do you do that?

thanks in advance

If I understand what you are saying, I think the easiest way is to composite the CG images with the original footage. The easiest way to do this is to render out a series of images that are the same size and shape of the original footage. Just make sure to render in something that has an alpha channel, like PNG format. Then simply layer the sequence of images over your original film in a different editor and you’re all done.

As a rendered video is 2d you can’t really put images “into” one, but with careful camera control you can make a newly rendered object appear to be in the scene. Of course, the longer the scene the harder it is to match all of the camera moves exactly.