Question show video on tracked image( arfoundation)

Hi, i trying make app unity can show video on tracked image.
my result in here: https://drive.google.com/file/d/1hpJxOBOALP_NMuvJ8l7jUNBfaZ2e3wLV/view?usp=sharing

but i have a trouble. i cannot place canvas ( all button) inside video. Canvas only anchor one place on screen.
how can i place canvas inside video?

under this post is my prefab and my app.