What file format is inside engines? DDS?

Hi there, here’s questions:

  1. When you add a texture, let’s say a .png image into engines (Unity, Unreal, other custom engines), the engine will convert that .png into its own format, right? What kind of type would that be? Is it always be DDS or every engine have their own format?
  2. Is only DDS can save mipmap? If one image will generate mipmap, it will always be DDS?

Thank you

yes DDS with a compression.