Making Alpha video 16:9 instead of a square


I been working on ZapWorks Studio for awhile now.
And now I trying WebAR with alpha video. The thing is that my video is 16 by 9, but the colorTexture and maskTexture seem like only in square, and can’t be modified to fit in the resolution I wanted.

Is there anyway I can fix or improve on this?

Edit: I been following the " Studio | Embedding Alpha Video (" tutorial.