When the video inside the <video> element plays, the video (or part of it) should also be visible on the canvas (below the video).
I'm observing a bug in iOS where a video texture isn't displayed inside a WebGL context of the canvas. It only becomes visible if the canvas is resized. Click the canvas, and if the video wasn't visible inside it, it'll become visible.
The video in the canvas worked for me with no clicking in iOS 12.0.1 (16A404), but stopped working in iOS 12.2 (16E227).