How to add custom post template selection list to Casper?

Before I explain what I need, please refer to the below Snapshot.

image

I am using the Casper theme and I have made a lot of changes to it. Now I need to add the post template as the above snapshot. I need the below templates.

  1. Default
  2. Video

The Video template should be like this.

How to do this? I have seen this in Simply and Mapache themes created by @GodoFredoNinja

Can someone help me, please?