Importing Video with Alpha Channel

Have you searched the Docs and Knowledge base? yes
Principle Version: 5.9
macOS Version: Mojave
Sketch Version: n/a
Description of what you need help with:
I’m trying to import video into principle. .mov files don’t seem to work. Mp4 files work, but I need to bring in a video with an alpha channel so the back is transparent.

Is this even possible? Any help would be greatly appreciated.

Screenshots/Sketch File/Principle file: (if applicable)

the mp4 format do not have an alpha channel. You will need to use a pro res video file, which supports alpha channels.