In WebGL it is possible to use a HTML5 Video element as the source of a texture. See for example https://developer.mozilla.org/en-US/docs/Web/WebGL/Animating_textures_in_WebGL

Canvas3D could support this too, by allowing passing elements like MediaPlayer or Camera to texImage2D, similarly to how VideoOutput gets associated with them via its source property.

In practice there are a few complications since this effectively means reimplementing more or less an equivalent of VideoOutput and the related backend stuff inside Canvas3D, but with a little effort we could probably make this flexible enough so that we share most of the code.

Alternatively, using QSGTextureProvider and a layer.enabled: true; visible: false VideoOutput element may work too and could be much simpler.