How can I combine an animation with transparent background and a pre-rendered scene(panoramic camera)(VR Video)?

Question

I have an animation where the camera is focused on a table and some experiment is going on. I want a classroom surrounding, the end result being a VR video, where I move my head to see the class as well as the animation going on at the table. Is it possible to render the experiment animation happening on the table with a transparent background (camera in panoramic setting) and then combine it with the classroom scene that I render separately. Otherwise, I'd have to place the table in the classroom and render out all the details of the classroom for every frame of the animation.

The first image is the table on which some experiment related animation will go on. That's the part i want rendered with a transparent background i.e only the table and whatever's on it.

The second image is the panoramic view of the classroom, that I want to render separately and then somehow merge the previous animation with this.

PS: The scene is downloaded from the blender website for the purpose of explaining my query.

Answer 1

To render Transparent Video from blender if I got you right

Follow the setting marked with Red box

The Container matters, and the PNG Codec works with transparent video.

And don't forget to thick the Transparent at the below box

If this didn't help, don't hesitate to ask for more.

Answer 2

To lay the Video clip on the Background

The picture above will be the result.

Node Setup

Switch to Compositing, and click on Use Node Set it up like this.

Step by step of setting your node To get the Viewer

To get Alpha Over

To add your Image

To fit your Image to Scene Size

I use Render Layer, But in your case, you need to load the clip to Motion Tracking since you have rendered it. Then you need to Add Movie Clip from the Compositing Panel as indicated, and replace it with my Render Layer Node